While Ukrainians wake up to the fourth day of the conflict, the country's minister of defence is asking the world to strengthen its support for Ukraine.

Oleksii Reznikov says that the country's "72 hours of resistance" has proven to the world that it is possible to repel Russian aggression.

Kyiv says it's establishing an "international" legion for foreigners wishing to volunteer in support of Ukraine.

"This will be the key evidence of your support for our country," remarked President Volodymyr Zelensky in a statement issued just now about Ukraine's new "foreign legion".

As we've reported, Russia's forces from Crimea have been making large advances on cities in Ukraine's south.

In Mykolaiv, a city located between Odesa and Kherson, the mayor Alexander Senkevich has announced this morning that the city remains under Ukraine's control.

However, there has been fighting overnight. One video being shared on Ukraine Telegram channels showed damage to buildings and streets in Mykolaiv's central streets.

There are now reports of fighting in the streets of Kharkiv. Russian troops broke into the city in the past hour, local officials say.

Social media footage appears to show some Russian units in the city. There are also pictures appearing to show at least two Russian "Tiger" vehicles on fire in the city.

The BBC has not yet verified these pictures.

Kharkiv officials this morning have warned locals to stay in shelters and off the streets.

There are now reports of a blast heard to the west of Kyiv city centre. It was after an air raid siren went off in the last hour or so.

Good morning to our readers in the UK and Europe. If you're just joining us, here's a round-up of what's happened in the last few hours as Russia's invasion of Ukraine continues into its fourth day:

• Despite warnings last night that Kyiv would come under attack from Russian missiles, an aerial blitz does not seem to have happened
• Explosions were however heard near the city and an oil depot in Vasylkiv to the south of the capital was hit and set ablaze, according to the local mayor. The fire prompted fears of toxic fumes and residents were warned to close their windows and stay indoors
• The southern city of Nova Kakhovka has been taken over by Russian troops, the city's mayor said this morning

• Meanwhile, Russian vehicles have entered Ukraine's second-largest city, Kharkiv, say Ukrainian officials. A loud explosion was also heard earlier in the city, where a gas pipeline is said to have been hit
• Residential areas in Kharkiv were also attacked, according to emergency services. A woman was reportedly killed and dozens were evacuated from a nine-story building
• At least six civilian deaths were also reported in the town of Okhtyrka, north-eastern Ukraine, according to the region's mayor

• In the last hour the BBC's Ukrainian Service reported new accounts of blasts in Kharkiv and Kherson in the south-east

• In a move to punish Russia, the EU, US and their allies will be cutting off a number of Russian banks from the main international payment system, Swift. They will also freeze Russia's central bank's assets
• Australia became the latest country to announce it will fund the supply of lethal weapons to Ukraine to help it fight Russia. The move comes after Germany decided on Saturday to supply weapons to Ukraine, representing a major policy shift

A city in Ukraine's south has been taken over by Russia, Ukrainian media is reporting.

Russian troops now occupy Nova Kakhovka, or New Kakhovka. It's a small city but one strategically located on the Dnieper River which directly supplies the Crimean peninsula with water channels.

Its mayor Volodymyr Kovalenko has reportedly said that Russian troops have seized the city's executive committee and removed all Ukrainian flags from buildings.

Analysts have noted that Russia's advance from the south have been the most successful so far, with Russian forces threatening Kherson, Mykolaiv and Melitopol.

Russian forces have entered Kharkiv, Ukraine's second-largest city, local officials say.

The head of the Kharkiv regional administration, Oleg Sinegubov, said that light military vehicles had "broke into the city".

Prior to his statements, footage had appeared to show some Russian military cars driving around on the streets of the north-eastern city.

Sinegubov urged residents to stay inside, saying Russian troops appeared to be in the city centre.

"Do not leave shelters! The Armed Forces of Ukraine are eliminating the enemy. Civilians are asked not to take to the streets."

Ukraine's State Emergency Service has confirmed a rocket struck a nine-storey unit block in the north-eastern city of Kharkiv, killing one woman and injuring others.

A few hours ago we also reported that a rocket had struck a gas pipeline in the same city. Kharkiv - Ukraine's second-largest city - has faced Russian military assault since 24 February, the first day of the war.

In just the past hour, the BBC's Ukraine service has also reported accounts of new blasts in Kharkiv and in Kherson - a south-east city.

Image source, Getty Images

YouTube's parent company Alphabet says it will suspend monetisation on its platforms for Russian state media outlets.

That means Russia Today (RT) and other channels can no longer receive money for ads on YouTube or other Alphabet-run websites and apps.

The company also says these outlets can no longer buy ads through Google Tools, place ads on Google services or otherwise use its ad technology to generate revenue for themselves.

A spokesman attributed the decision to "extraordinary circumstances" and said Alphabet would "take further steps if necessary".

It comes after Ukraine's Digital Transformation Minister Mykhailo Fedorov said he had asked YouTube to block Russian propaganda.

State media - RT in particular - make millions of dollars per year through ads on YouTube and elsewhere on Google services.

Facebook and Twitter have already suspended ads from Russia. The country has restricted access to both platforms.

It's about 7.30am in Kyiv. Despite warnings last night that the capital would come under attack from an onslaught of Russian missiles, an aerial blitz does not appear to have happened - although there have been explosions just outside the city.

Authorities said a Russian strike hit an oil depot in Vasylkiv, a city just south of Kyiv which also has a military airbase. The fire there is still raging, and officials have warned residents in the surrounding area as well as in Kyiv to close their windows against the chemical fumes.

Kyiv's deputy mayor Mykola Povoroznyk has said this morning the situation in the city remains calm and under the control of Ukrainian forces.

He noted though there'd been clashes with Russian saboteur groups in Kyiv overnight, but did not give any details.

Image source, Getty Images

Ukraine's government is framing the country's resistance toward Russia as a fight to secure the future of Europe.

In a lengthy post on Facebook, Defence Minister Oleksiy Reznikov lauded soldiers, police, medical staff, and also civilians who have taken up arms.

"Take a look around. Many have finally conquered fear and dared to challenge the Kremlin," Reznikov wrote.

He added: "Where are all those who promised to capture Kyiv in two hours? I can't see them."

He said that while challenges remain, people all over the world are watching closely and "help that was impossible three days ago is now on the way".

"Without this army and our people, Europe will never be safe. Without us Europe simply won't [exist]."

Sumy Governor Dmitry Zhivitsky says at least six Ukrainians - including a seven-year-old girl - died as a result of a Russian attack on Friday on the northeastern city of Okhtyrka.

A kindergarten and an orphanage were among the reported targets, which Russia has denied.

Ukraine's Foreign Minister Dmytro Kuleba has alleged "war crimes" were committed and has called for an investigation into the incident by the International Criminal Court.

On the day Vladimir Putin ordered his soldiers into Ukraine, Arina had planned a dance class after work and then a party. Three days later, the English teacher was making Molotov cocktails in a park.

I found her crouching on the grass with dozens of other women, grating polystyrene chunks as if they were cheese and ripping sheets into rags for homemade bottle-bombs.

Such scenes are unimaginable to most in Europe. They were unthinkable here too, once.

But Dnipro is now preparing to defend itself against advancing Russian troops.

"No-one thought this is how we’d spend our weekend, but it seems like the only important thing to do now," Arina told me, the young teacher’s face and hair sprinkled in white dust from the polystyrene.

"It’s pretty terrifying. I think we don’t really realise what it is we’re doing; we just need to be doing something," she said.

A few metres away, Elena and Yulia told me they’d left their children with grandparents in order to come and help make these weapons.

"Sitting home doing nothing would be even scarier," Elena said, not pausing her grating even for a second.

She laughs and says that she’s a good cook, and this process is not so different.

"I can’t believe this is happening to us, but what choice do we have? No-one consulted us on anything," Elena said.

Read more from Sarah in Dnipro here.

There are now reports that air raid alerts have gone off in at least two Ukrainian cities: Rivne in the west and Lutsk in the northwest.

People have been advised to seek shelter.

It is just past 06:00 local time on the ground.

Hacker group Anonymous claims they have disabled Chechnya's government website 12 hours after the Russia-allied region said it was sending troops into Ukraine. A BBC check found the site currently shows a 404 Host Not Found error page.

Chechnya, officially the Chechen Republic, is a constituent republic of Russia. Its leader, Ramzan Kadyrov, is a close ally of Vladimir Putin.

Anonymous declared a "cyber war" against Russia on Friday, and has launched several cyber attacks on Russian government websites, including taking down the Russian Ministry of Defence website for a few hours.

State media outlet Russia Today or RT.com has also confirmed that its sites were slowed down, with some disabled, in an attack on Friday.

The BBC's international correspondent Orla Guerin earlier shared this dispatch from Kyiv. She spoke with locals who'd formed volunteer brigades to assist the army effort.

"I don't want to live in Russia and my brothers in arms don't want that either," one of them said. "We will defend this city or I will die."

Another woman, walking her dog on the deserted streets, told our correspondent: "We demand an end to the war. We can do it with sanctions."

Watch the full three minute report below.

Ukraine's prime minister has thanked Western allies after their decision to remove certain Russian banks from the Swift messaging system.

"Grateful to all our partners I talked [to] today," PM Denys Shmyhal wrote on Twitter.

"Appreciate your support and real help in this dark time. Ukrainian people will never forget this!"

Image source, Getty Images

Australia says it will fund the supply of weapons to Ukraine to help it fight Russian forces.

The move comes days after the government in Canberra said it would only provide “non-lethal” military equipment.

Prime Minister Scott Morrison joined Ukrainian-Australians at a church service in Sydney on Sunday morning before announcing the decision.

“The Australian government will continue to stand up for what is right when it comes to Ukraine,” he said.

"We’ll be seeking to provide whatever support we can for lethal aid through our Nato partners, particularly the United States and the United Kingdom."

PM Morrison added that the rapid processing of visa applicants from Ukraine would be a "top priority" for him going forward.

Australia’s contribution adds to the significant amounts of weaponry and ammunition already being supplied to Ukraine by the US, UK and other Nato allies. Germany, in a significant move, yesterday overturned a long-held stance not to supply lethal aid.

CNN is reporting that a six-year-old boy was killed in crossfire in western Kyiv earlier tonight. He would be the youngest casualty of the war so far.

Several others were also injured in the clashes in Kyiv. CNN have cited the report to Okhmatdyt Hospital in the city.