Image source, Getty Images

As we have been reporting, Russia's expected new offensive in eastern Ukraine has begun.

Russian forces

For several weeks, Moscow has been concentrating reinforcements – new units and damaged units from north-eastern Ukraine – in the Donbas region, according to the Institute for the Study of War (ISW).

US officials say Russia now has 76 battle groups in the east, having added 11 to the area in recent days. They typically comprise 700 to 900 soldiers plus military equipment.

Another way to put it is there are some 70,000 Russian troops in Donbas, according to Ukrainian estimates.

Russian Security policy expert Dr Aglaya Snetkov points out there are some battle groups committed to the area around the devastated southern port city of Mariupol.

If that key city falls, it would allow those forces to move north and join the fight in Donbas, which could be important but maybe not decisive, Snetkov says.

Image source, .

Ukrainian forces

While we have estimates of Russian force numbers from Western agencies, Ukraine and Russia itself, we've heard much less about the size of Ukrainian forces and losses, Snetkov says.

This is partly because Ukraine does not want to share this information in case it could be of advantage to its enemy, and the West seems to be following an unspoken agreement to be silent on this, she says.

At the start of the war Ukraine had 10 brigades in the east of the country, regarded as the best-equipped and best-trained soldiers the country has.

Military equipment

The Ukrainians have the manpower but lack military equipment, whereas Russian forces have sufficient military equipment but lack manpower, Snetkov says, given the traditional view that attacking forces need overwhelming numbers.

The battles in the east are likely to differ from earlier battles around Kyiv, more closely resembling conventional World War Two combat, with trenches, and heavy equipment such as tanks, Snetkov says.

Russian forces could gain ground with heavy concentration of artillery and numbers, but a dramatic success is unlikely, according to the ISW.

Image source, .

If you're just joining us, here's a summary of the day's events in Ukraine so far:

• Ukraine's President Volodymyr Zelensky says the expected large-scale Russian offensive in the eastern Donbas region is under way
• Russian forces are attacking Ukrainian positions along the entire 300-mile (480km) front line in the eastern Donbas region

• Ukraine says Russian forces have seized control of Kreminna, in the Luhansk region
• Russia says it struck more than 1,000 targets in the Donbas overnight
• In Mariupol, Russian-backed fighters are reportedly trying to storm an industrial complex in Mariupol where Ukrainian troops, along with civilians, are said to be holed up
• Ukrainian forces are making some successful counter-attacks south of Kharkiv, according to military analysts
• The UN says five million people have fled Ukraine since the war began

Image source, EPA

Russia will not use nuclear weapons in Ukraine, Foreign Minister Sergei Lavrov says.

Asked about the issue in an interview with TV channel India Today, Lavrov says: "Conventional weapons only."

Early on in the war, Vladimir Putin ordered Russia's nuclear forces be placed on high alert, and a number of Russian government figures have signalled the country would be willing to use them in certain circumstances.

Lavrov also says, with Russia's offensive now focused on Ukraine's east, the war is entering a new phase, echoing similar comments from the Ukrainian military.

"The operation in the east of Ukraine is aimed, as was announced from the very beginning, to fully liberate the [self-proclaimed] Donetsk and Luhansk republics. And this operation will continue," he says.

"Another stage of this operation is beginning, and I am sure this will be a very important moment of this entire special operation."

Jessica Parker
BBC News

Image source, Getty Images

The European Commission says it’s “definitely working” on possible further sanctions against Russia “in the field of oil".

But Chief Spokesman Eric Mamer says he can't give further details for the moment.

The EU has so far approved five sanctions packages but it’s unclear if and when a sixth could be passed.

Earlier, French Finance Minister, Bruno Le Maire, reportedly said: "I hope that in the weeks to come we will convince our European partners to stop importing Russian oil."

Speaking on French radio Europe 1 he said, "What has been the primary source of currency for [Russian President] Vladimir Putin for several years? It is not gas. It is oil".

Le Maire made a similar call earlier this month.

Read more on sanctions on Russia here.

Adam Easton
Warsaw Correspondent

The latest now from the situation in Ukraine's neighbour Poland, where the majority of refugees have fled and Polish PM Mateusz Morawiecki says Poland is ready to treat up to 10,000 Ukrainian soldiers in its hospitals if required.

Morawiecki says several dozen Ukrainian soldiers are currently being treated in Polish hospitals.

He's speaking after opening the first “container town” for internally displaced refugees in the western Ukrainian city of Lviv.

The temporary accommodation can shelter between 300 and 500 women and children fleeing the fighting in eastern Ukraine, the prime minister’s office says.

Morawiecki has been meeting women and children besides rows of metal containers, each containing a small room for refugees who have nowhere to stay.

In co-operation with the Ukrainian authorities, the Polish government plans to house up to 5,000 internally displaced refugees in the temporary container towns in Lviv.

There are plans to set up similar accommodation near the capital Kyiv, Morawiecki’s office says.

Almost five million Ukrainians have fled the war since Russia's invasion, the United Nations says, in the fastest-growing refugee crisis in Europe since World War II.

Women and children make up around 90% of those who have fled. Men aged 18 to 60 are eligible for military call-up and are unable to leave the country.

Almost two-thirds of all Ukrainian children have been forced from their homes, including those still inside the country, the UN says.

More than 2.8 million Ukrainian refugees are now in Poland.

UN refugee agency (UNHCR) figures show nearly 645,000 Ukrainians fled in February, with nearly 3.4 million doing so in March and 945,000 leaving so far this month.

"The key is that the borders remain open, people can access safety and when they get to the neighbouring countries they have access to assistance," UNHCR spokeswoman Shabia Mantoo told reporters in Geneva.

Image source, SERHIY HAIDAI/LUHANSK OVA

More now from Luhansk regional administrator, Serhiy Haidai, who has urged locals to evacuate immediately from the region as Russian forces continue their assault.

Earlier, he said 50 people had been evacuated from the eastern cities of Lysychansk and Severodonetsk in the Luhansk region and taken to safety.

"Today we will take everyone out," he posted on Telegram.

Ukrainian troops have left the city of Kreminna in eastern Ukraine and taken up new positions, Reuters quoted Haidai as saying.

"Kreminna is under the control of the 'Orcs' [Russians]. They have entered the city," Haidai told a briefing.

"Our defenders had to withdraw. They have entrenched themselves in new positions and continue to fight the Russian army."

He said Russian forces had attacked "from all sides".

More now on the military assistance that's being sent to Ukraine to support its defence of the Donbas region.

Military analyst Justin Crump tells the BBC it's a race against time to get the supplies to where it is needed. Once the military equipment enters Ukraine from the west it still has to make its way to the Donbas in the east, without being intercepted by Russia.

There are also technical logistics to overcome, says Crump, because Nato artillery rounds are different to the ex-Soviet systems traditionally used by Ukraine.

Crump, who was a British Army tank commander, expects to see "hard fighting" in the eastern region. He says Ukraine could overcome its lack of resources by using the "clever tactics" it has employed before.

However, Crump thinks Russia has learned "some significant lessons" from earlier in the conflict. "This is going to be a much more evenly balanced fight than we saw around Kyiv", says Crump.

Read more here about military aid sent from the US to Ukraine.

Talking about the new offensive from the Ukrainian point of view, an aide to President Volodymyr Zelenskiy says Russia's action in the east will fail because Moscow's forces lack the strength to break through Ukrainian defences.

"The battle for Donbas, which was announced and apparently began yesterday, is under way and is going very cautiously," presidential adviser Oleksiy Arestovych says, as quoted by Reuters.

"The battle will not go in Russia's favour."

Image source, EPA

Russia's Defence Minister Sergei Shoigu has claimed the US and other Western countries are "doing everything to drag out Russia's military operation in Ukraine".

Shoigu says the increasing volume of foreign arms supplies to Ukraine "clearly demonstrates their intentions to provoke the Kyiv regime to fight to the last Ukrainian standing".

He adds Russian forces are methodically carrying out a plan to "liberate the Donetsk and Luhansk people's republics", in a reference to the self-proclaimed rebel entities in eastern Ukraine.

Shoigu, 66, was shown on Russia's state Rossiya 24 TV channel, which said the minister was speaking at a collegium (an advisory board) with the country's top military officials in Moscow.

It was not clear whether the meeting was broadcast live or pre-recorded.

If confirmed, this would be Shoigu's first public appearance in days, amid reports he might have some health issues.

Image source, Mariupol city council via Reuters

If you're just joining us, or need a recap, here is a summary of today's key events in the war.

• Ukraine's President Zelensky says the expected large-scale Russian offensive in the eastern Donbas region is under way
• Russia's forces are attacking Ukrainian positions along the entire 300-mile (480km) front line in that key region, Ukraine says
• Russia claims to have struck more than 1,000 targets in Donbas overnight
• Ukraine says Russian forces have seized control of Kreminna, in the Luhansk region.
• In the devastated city of Mariupol, Russian-backed fighters are reportedly trying to storm an industrial complex where the last Ukrainian defenders are holed-up, along with civilians

• A Zelensky adviser tells the BBC that with the right heavy weaponry - such as tanks and artillery - Ukrainian forces can beat this renewed offensive

Image source, Getty Images

Russia has moved most of the focus of its war to eastern Ukraine, after pulling back its forces from near the capital Kyiv.

Ukraine's leader Volodymyr Zelensky says the battle for the area known as Donbas has begun and a very large part of Russia's army is taking part.

What is Ukraine's Donbas?

When President Putin talks of Donbas, he is referring to Ukraine's old coal and steel-producing area. What he really means is the entirety of two big eastern regions, Luhansk and Donetsk, which run from outside Mariupol in the south all the way to the northern border.

These areas are broadly Russian-speaking and Mariupol was one of the most pro-Russian cities in Ukraine.

But Russian forces have besieged Mariupol since the invasion, levelling much of the city.

Why does Putin want to control it?

The Russian leader has repeatedly made the unfounded accusation that Ukraine has carried out genocide in the east.

When the war began, almost two-thirds of the eastern regions were in Ukrainian hands. The rest was run by Russian proxies, who created Moscow-backed statelets during a war that began eight years ago.

Just before the latest war, President Putin recognised all of the two eastern regions as independent of Ukraine.

If Russia were to conquer both big regions, it would give Vladimir Putin some sort of achievement from Russia's war. The next step would then be to annexe Donbas, just like he did with Crimea after a discredited referendum in 2014.

And if it came before 9 May, he would even be able to celebrate on Victory Day, when Russia's military still marks the defeat of Nazi Germany in 1945.

Russia's puppet leader in Luhansk has already spoken of having a referendum in the "near future", although the idea of even a sham vote in a war zone seems absurd.

Read in full: Why Russia is trying to encircle Ukraine's east

We've been hearing from an adviser to President Zelensky who says Ukraine can beat the renewed Russian offensive in the east with the right weaponry.

Ihor Zhovkva, deputy head of Zelensky's office, says Russia started heavy shelling with artillery yesterday, as its forces began the "concentrated offensive" in the east they've been planning.

He tells BBC Radio 4's Today Programme it's "very important for Ukrainian forces to have heavy weaponry", including artillery systems, tanks and armoured vehicles.

If Ukraine has these weapons, it will be able to withstand the Russian offensive and have victory in the eastern region, he says.

Zhovkva says arms shipments from the West are "getting better" – and the latest $800m batch of US military aid included "the items we really need".

Zhovkva adds that Donbas - where the latest offensive is taking place - is very important symbolically for Moscow, as it is where Russia began its "aggression against Ukraine" in 2014, capturing parts of the region and establishing "so-called republics" there.

Image source, Getty Images

Street battles are being reported in the eastern Ukrainian city of Kreminna.

Ukraine says Russian forces have seized control of Kreminna, which is in the Luhansk region.

The regional administrator, Serhiy Haidai, says four civilians in the town have died. He urged residents to remain in shelters.

He tells Ukrainian TV that heavy artillery fire left seven residential buildings in flames and targeted a sports complex where the nation's Olympic team trains.

Russians have been destroying buildings along the way, he says, adding that his forces retreated to regroup and keep fighting.

Russia's military are attacking along a 300 mile (480km) front in eastern Ukraine as part of its major offensive in what Ukraine has called "a new phase of war".

Ukraine’s General Staff says Russian forces are focusing their efforts on taking full control of the Donbas region, in the east.

Russian forces have tried to break through Ukraine's defences along nearly the entire frontline, the General Staff said in a statement.

So far, Russian forces have only managed to pass through two areas - the eastern town of Kreminna and another small town, Luhansk regional military administrator Serhiy Haidai says.

Russia began stepping up its full-scale assault yesterday, focusing on the Donbas regions of Donetsk and Luhansk, with forces trying to advance in several sections, including from the neighbouring Kharkiv region.

The General Staff said the Russian military continues to block and shell the southern port city of Mariupol and fire missiles at other cities.

In its latest briefing, the Russian Defence Ministry says missile and artillery forces struck 1,260 targets in Ukraine overnight.

It says "high-precision air-based missiles" hit 13 Ukrainian positions in parts of the Donbas, including the key town of Slovyansk.

It also says other air strikes "hit 60 military assets of Ukraine", including in towns close to the eastern frontline.

Russian anti-aircraft forces downed a Ukrainian MiG-29 jet in the Donetsk region, the ministry said.

The BBC can't independently verify the ministry's claims.

Image source, .

We have more from Dr Jack Watling of Rusi speaking on the Today programme about the Russian offensive in the Donbas and whether Russia can take control of that region by 9 May - the date when it holds a parade in Moscow to mark its victory in World War Two.

"It's feasible, but it's a very long way from being assured. The Ukrainian military had to withdraw a lot of units from the areas that defend Kyiv and their units are very tired, and so it's going to be a really hard fight... the Ukrainians risk taking a lot of casualties in this fight (in order) to blunt that advance."

On the other hand, it is probably the last push for the Russians until they really have to pause for a couple of months to rebuild their forces, he says.

The 9 May date has shifted in its significance, he adds.

Image source, Mariupol city council via Reuters

Special forces are now storming Mariupol's Azovstal iron and steel works plant, where the final Ukrainian troop holdouts are sheltering, a Russian-backed separatist official in the eastern Donbas region says.

Eduard Basurin, who represents the self-proclaimed Donetsk People's Republic (DNR), tells Russia 24 TV channel that specially selected "assault groups" are being helped by Russian aviation and artillery.

Basurin also denies reports by Ukrainian officials that many civilians, including children, are hiding at Azovstal - a huge industrial area in the city centre.

Last week, he said the Ukrainian troops should be "smoked out" from the plant, in what a number of military experts in Ukraine and the West said was a veiled threat to use chemical weapons.

The Ukrainian defenders later said the Russians dropped an unknown "substance" from a drone - but this claim has not been independently verified.

Mariupol, a strategic port on the Sea of Azov coast with a population of more than 400,000 before the war, has been besieged by Russian troops since early March.

The city's authorities say Mariupol has been razed by heavy shelling and air strikes, and that thousands of civilians have died.

Image source, Reuters

Dr Jack Watling, of defence and security think tank the Royal United Services Institute (Rusi), reflects on how this phase of the war - with the Russian offensive in the Donbas - will be different from what we've seen in recent weeks.

During their offensive on Kyiv, the Russians were advancing on two roads, and struggled to get off those roads - because of marshes and dense woodland, he tells BBC Radio 4's Today programme.

While their artillery was stuck quite a long way from the front in that traffic jam, their forward units were in range of Ukrainian artillery, and they took very heavy casualties whenever they tried to move.

"This, by contrast, is a fight over quite open country, over a very wide area and there are parts of it that are quite industrial and urbanised... the towns are smaller," he says.

So the Russians should be able to be less fixed, to manoeuvre, and there should be much more in the way of contact battles (units clashing into one another directly) rather than ambushes, he predicts.

The leader of the last Ukrainian soldiers in the devastated port of Mariupol has urged world leaders to arrange safe passage for civilians sheltering at a giant steelworks.

Local officials say a thousand people - many of them relatives of the fighters - have taken refuge in bunkers and tunnels at the site.

Reports from the besieged southern port say separatist fighters supported by Russian forces are trying to storm the industrial complex.

Russia's military says it controls almost all of Mariupol and over the weekend the city's last defenders ignored a Russian deadline for surrender.

Capturing the whole of the city would be a major strategic prize for Russia, leaving it in control of a vast swathe of southern and eastern Ukraine.

Image source, .