Eyewitnesses have also told BBC Ukrainian that they heard explosions in the western city of Ivano-Frankivsk.

Ukrainian news outlets are also reporting similar blasts.

Several eyewitnesses have told BBC Ukrainian that they heard explosions in the region of western city of Lviv.

The UNIAN news agency has also cited social media users who have reported two strong explosions in the city.

According to local media reports, air raid sirens went off throughout the night in Lviv and many other regions in Ukraine.

The Kyiv Independent meanwhile says there are reports that Lviv is under Russian missile attacks.

The cause of the explosions is still unknown, and the BBC cannot confirm eyewitness accounts.

We'll bring you more information once we know more.

Lviv is a stronghold in western Ukraine where many foreign media teams are currently based, and a city where many refugees are passing through on their way out of Ukraine.

Image source, EPA

Refugees have continued to stream into Moldova, prompting the country's leader to call for international assistance to cope with the influx.

“We now have over 270,000 people who have crossed the border," Moldova Prime MInister Natalia Gavrilița has told the BBC World Service.

"More than 100,000 people who have chosen to stay – at least temporarily. For a country like Moldova these are quite high numbers. “

Moldova, a small country of about 2.5 million sandwiched between Ukraine and Romania, is one of Europe's most economically fragile. The number of Ukrainian refugees represent about a 4% increase in their population.

Image source, Getty Images

Image source, Getty Images

Ms Gavrilița added that Moldovan civilians are helping to house and care for the refugees that are arriving by the thousands every day.

“We are very worried about the economic consequences of the war... which is hitting particularly hard a country like Moldova, one of the poorest in Europe," she said.

"We certainly need outside help.”

Image source, EPA

Image source, EPA

A drone was brought down by Ukrainian security forces in Kyiv on Saturday afternoon, according to officials and witness reports.

The drone was said to contain a three kilogram explosive. It crashed in the Podil neighborhood of Kyiv, sparking a small fire at a bank.

Geolocation of the images were verified by the BBC.

Image source, Getty Images

A senior Vatican official has expressed concern that Russia's invasion of Ukraine is an indication that the world is "falling back into the past instead of daring to take steps towards a different future".

Vatican Secretary of State Cardinal Pietro Parolin, widely viewed as the second most powerful man in the Catholic church after Pope Francis, called on Russia to enter into negotiations with Ukraine, saying that leaders "who wage war rely on the diabolical logic of weapons and forget humanity".

He repeated the Vatican City's offer to host mediation talks, and said that it is important to take steps towards "a future of peaceful coexistence".

"War is like a cancer that grows, expands and feeds on itself. It is an adventure with no return, to use the prophetic words of St John Paul II," Parolin said.

"Unfortunately, we must recognise it: we have fallen into a vortex that can have incalculable and ill-fated consequences for everyone."

"But I would also like to say that it is never too late, it is never too late to make peace, it is never too late to retrace one's steps and find an agreement," he added.

Lucy Williamson
BBC News

Image source, Getty Images

Moldova's foreign minister Nicu Popescu has told the BBC that his country is approaching a "breaking point" in its ability to shelter those fleeing the conflict in Ukraine.

Popescu has warned that his country is nearing the point where it will run out of buildings to house refugees, or the means to keep them warm and safe.

The number of refugees staying in Moldova is low by regional standards - just over 100,000 - but that represents a 4% increase in the national population and would be equivalent in proportion to 2.5 million refugees arriving in the UK in a fortnight.

Popescu told the BBC that Moldova was “Ukraine’s most fragile neighbour” with fewer financial resources, and less resilience in security, health care and education.

A full Russian assault on Ukraine’s third largest city of Odesa, 30 miles (48 kilometres) from Moldova’s border, would likely trigger an “overwhelming” influx of refugees.

He added that it would be a “complete catastrophe for the humanitarian situation".

Image source, Reuters

If you're just joining us, here's a recap of what's been happening in Ukraine as Russia's invasion reaches its 18th day:

• Some 1,300 Ukrainian troops have died in the conflict so far, Ukrainian President Volodymyr Zelensky has said
• In Mariupol in the south-east of the country, Moscow's forces have made further gains, capturing the eastern outskirts of the port city. Satellite photos taken on Saturday by a private US company showed extensive damage to residential and civilian infrastructure in the city

• Ukrainian officials have also confirmed that their forces have left the small nearby city of Volnovakha, which they say has been completely destroyed
• But in the occupied city of Melitopol, Russian troops have faced a huge protest from residents against the abduction of Mayor Ivan Fedorov President Zelensky called his kidnapping a "war crime"
• Elsewhere, Ukrainian officials have claimed that Russian troops fired on a convoy of women and children evacuating a village near Kyiv, killing seven people. Moscow has yet to comment on the allegations
• Polish Border Guards have said that more than 1.6 million people have now fled Ukraine to Poland since the conflict began more than two weeks ago
• Meanwhile, French President Emmanuel Macron has said that Russian President Vladimir Putin did not show any willingness to end the war in Ukraine during a 75-minute phone call between the French, German and Russian leaders
• And Russia's deputy foreign minister has warned the West that arms convoys delivering weapons to Ukrainian forces could become "legitimate targets" for Moscow's troops
• Read what happened on day 17 of Russia's invasion here.

Image source, EPA

People in the UK who offer homes to Ukrainian refugees will receive a "thank you" payment of £350 per month, the UK government has announced.

Under the Homes for Ukraine scheme, people will be able to nominate a named Ukrainian individual or family to stay with them, or offer a separate property for them to use rent-free.

Those offering accommodation will be vetted, and will need to commit to a minimum of six months.

But the Refugee Council - a charity that supports refugees and asylum seekers - says the scheme falls short and doesn't offer people enough support.

And the Labour opposition accused the government of dragging its feet, saying many questions remain unanswered - particularly around vulnerable children and older people.

Read more on the scheme, and reaction to it, here.

Image source, Telegram/SES

Russian shelling in the cities of Severodonetsk and Rubizhne in the Luhansk region has damaged dozens of apartments and sparked massive blazes, according to the Ukrainian State Emergency Service (SES).

Around 60 buildings, including private homes and apartment buildings, were hit overnight, according to government estimates that have not been independently verified.

"The enemy will not break the Luhansk region!" the SES posted on its Telegram channel, adding: "Let's hold on! Everything will be UKRAINE!"

The news comes as air raid sirens are sounding throughout most of the country, according to the Kyiv Independent.

"Air raid alerts in almost every region of Ukraine," the newspaper posted online around 04:00 local time (02:00GMT).

Residents have been asked to seek shelter immediately in cities including Lviv, in western Ukraine, and Poltava - a central eastern city where thousands of evacuees have recently fled from frontline cities.

Image source, Getty Images

The regional council in the occupied city of Kherson has voted to adopt a resolution affirming that the city remains Ukrainian, local officials have said.

The vote comes amid accusations by Ukrainian officials that Russian is planning a "pseudo" referendum on creating a breakaway "people's republic".

Yuriy Sobolevskyi, the deputy head of the council, said in a Instagram post that members of the body "accepted the appeal that Kherson region is Ukraine" by 44 votes.

He wrote that deputies could "never recognise attempts to create a 'people's republic' in the Kherson region and seize part of Ukraine".

"Kherson region was, is and will be an integral part of a single state - Ukraine," he added.

Foreign Minister Dmytro Kuleba tweeted earlier on Saturday that "Russians [are] now desperately try to organise a sham 'referendum' for a fake 'people's republic' in Kherson".

"Severe sanctions against Russia must follow if they proceed. Kherson is and will always be Ukraine," he wrote.

Image source, Ukrainian Orthodox Church

A centuries-old Ukrainian Orthodox monastery in eastern Ukraine was heavily damaged after barely escaping a direct hit from an explosive shell, according to a statement from the church.

On the evening of 12 March, an aerial bomb exploded near a bridge by the Sviatohirsk Lavra, in Donetsk, destroying almost all of the windows at the monastery and damaging several buildings.

Multiple people, including monks and evacuees sheltering inside, were wounded and transported to hospital. There were no reported deaths.

The monastery cellars are now housing some 520 refugees, according to online newspaper Ukrayinska Pravda. About 200 are children.

Jeremy Bowen
BBC News, Kyiv

The recruits were like any bunch of young lads who had decided they were no longer boys.

Most of them were in their late teens, not long out of school. After three days' basic training, they would head for the front line - or very close to it.

Some were wearing knee pads that looked too small, as if they had come with skateboards on their 12th birthdays. A few had sleeping bags. One had a yoga mat.

One week later, they were in uniforms, body armour, proper infantry kneepads and helmets.

"We just have to stop them here, because if they get to Kyiv this war might be over," said economics student Dmytro Kisilenko, 18.

He was "not much" scared, he said. "But it is human nature to feel scared, and of course deeply in my soul I feel a bit scared, as no one wants to die, even if it's for your country".

"So, death is not an option for us".

Read more:

'No one wants to die' - meeting Ukraine's teenage soldiers

Tens of thousands of Russians have left the country since the invasion of Ukraine.

They're mostly young and liberal - they're shocked by the war and economic sanctions, and are concerned by the latest crackdown on dissent led by President Putin.

An estimated 25,000 of them have moved to Georgia. Yevgeny is one of them.

Image source, Getty Images

US Vice President Kamala Harris has warned that the Russian invasion of Ukraine "threatens democracy and security across Europe" and "by extension, when democracy is threatened anywhere, it threatens us all".

Harris made the remarks on Saturday to fellow Democrats after returning from a state visit to Poland and Romania.

The Biden administration is facing pressure to give more muscular assistance to Ukraine, but has insisted that it will not take steps that could lead to direct conflict with Russia, such as by enforcing a "no-fly" zone over Ukraine.

The White House faces a challenge in confronting the Ukraine crisis - entering office, President Biden faced an American public reluctant for the US to become tangled up in foreign wars, and upon pulling out of Afghanistan last year, he declared that it was not America's place to help police the world.

However, polls suggest that the US public are increasingly paying attention to Ukraine, with as many as 45% supportive of a "no-fly" zone over the country.

Image source, Getty Images

Online auction site eBay has said that it is blocking all transactions involving Russian addresses.

"We stand with Ukraine and are taking a number of steps to support the Ukrainian people and our sellers in the region," a spokesperson for the California based company told the BBC on Saturday.

"As a result of service interruptions by payment vendors and major shipping carriers, we have temporarily suspended all transactions involving Russian addresses and transactions involving Ukraine addresses may experience delays".

Previously, eBay had waived seller fees for vendors in Ukraine, and is "protecting" them from late shipment penalties and negative reviews.

Customers in the US, UK, Canada, and Australia, also have the option of donating to Ukraine when purchasing items at checkout.

Guy Delauney
BBC Balkans correspondent

Image source, Getty Images

Authorities in Croatia expressed alarm over a military drone that crashed in the capital Zagreb on Thursday.

The country's prime minister, Andrej Plenkovic, has said he was concerned that the aircraft apparently flew from Ukraine without being intercepted by Nato.

Military investigators spent Saturday digging out what's left of the drone from the crater it caused in Zagreb. As they worked, students were evacuated from the dormitory which the unmanned aircraft narrowly missed when it came down.

The head of the military police said the drone's black box had been recovered intact. That could help investigators pinpoint who fired it - and to what end.

A Croatian military official confirmed that the drone was a Soviet-era TU-141. Despite its age, it's still being used by the Ukrainian military.

But officials in Kyiv have denied responsibility for the incident.

There's been widespread alarm in Croatia that a military drone could have reached Zagreb from Ukraine without being intercepted.

Image source, Getty Images

Ukrainian President Volodymr Zelensky has signed a decree to award the title of 'Hero of Ukraine', the highest honour given to individual citizens in the country, to eight military defenders.

Among them is the first woman to be posthumously given the title, according to the BBC's Ukrainian service.

Sergeant Derusova Inna Nikolaevna, a combat medic, saved more than ten servicemen in Sumy, risking her own life, Zelensky said.

She died from artillery shelling by Russian troops, helping the wounded.

Five of her comrades were also given the Hero of Ukraine title posthumously.

Image source, Getty Images

Russia's central bank has decided to keep the Moscow stock market closed to trading next week as Western sanctions continue to hammer every aspect of the national economy.

The Moscow Exchange will be closed from March 14 to 18, the central bank announced on Saturday.

The foreign exchange market, money market and repo market will remain open on those days, the statement said. A decision on trading next week will be made in the coming days.

If you'd like more analysis and expert opinion on the war in Ukraine, you can listen to the latest episode of Ukrainecast here.

Today's episode is presented by the BBC’s Fergal Keane from Lviv in western Ukraine, a city thousands of refugees pass through as they try to leave the country.

Fergal is joined by the BBC's Abdujalil Abdurasulov, who’s in Kyiv as Russian forces continue to slowly advance, and Kevin Connolly, former Moscow BBC correspondent.

They discuss Russia’s strategy to take Kyiv and who Russian President Vladimir Putin’s allies are.

The Belarus opposition leader Svetlana Tikhanovskaya, who’s living in exile, also explains why she feels her country’s future is so closely connected to the fate of Ukraine.

Russian troops have expanded their offensive across Ukraine as they continue attempts to encircle and cut off Ukraine's capital, Kyiv.

Kyiv is bracing itself for an assault, with Ukrainian forces and volunteers building new defences and creating barricades on major routes to slow any Russian attack.

Although Russian troops are now making gains on the outskirts of Kyiv, their progress in the north has been much slower than in the south.

The main advance towards the capital initially came from Belarus, down the west side of the Dnieper River via Chernobyl.