Poland says more than 670,000 people have arrived there from Ukraine since the Russian invasion began a week ago.

But the traffic is not all one way.

The BBC's Mark Lowen has travelled to the Polish border with Ukrainians - some who had no military experience - returning to their country to support the war effort.

Nick Thorpe
BBC News, Budapest

Emergency relief staff in Hungary have been inundated with donations from the public, and offers of private accommodation for refugees.

At Budapest West station, a constant stream of people bring everything from a bag of apples to a crate of clothes. It’s eerily reminiscent of the last refugee crisis, in 2015.

The pro-government media here emphasise that these refugees are different - all European, and Christian. That’s not strictly true.

Among those thronging the station are refugees from Africa, India, Bangladesh, Pakistan and Middle Eastern countries, who were all studying in Ukraine.

Several thousand foreign students were studying at Vinnitsa National Medical University in central Ukraine. Kharkiv is also a big university city.

Soon after 08:00 local time (09:00 GMT), a train loaded with refugees arrives from Zahony, on the border with Ukraine.

"First we take their bags, then we find them translators, and offer food and accommodation," says Reka Gilicze of Hungarian Reformed Church Aid.

Psychologist Anastasia, 20, left Kyiv with the six-week-old puppy she bought the day before the invasion. She fled when several buildings near her home were hit by explosions.

She says she’s seen many signs of post-traumatic stress disorder among those fleeing and praised the resolve of her country's people.

But she adds she has also witnessed ugly scenes on her journey - people pushing others aside in the panic to leave Kyiv, for one.

Russians face dilemma as covert plans failpublished at 19:01 Greenwich Mean Time 4 March 2022

19:01 GMT 4 March 2022

Gordon Corera
Security correspondent, BBC News

Russia’s initial political plans for Ukraine look to have gone wrong, just like those of their military.

However, that failure is raising fears over what tactics they may seek to use, with European intelligence officials warning of more repressive tactics as a result.

Over a period of years, Russia’s security service, the FSB, has been trying to recruit networks of agents across Ukraine who could be activated when an invasion began. They were expected to try to take over key institutions.

But hopes for some kind of a quick coup have faded. That may have been down to over-optimistic forecasts about the size and capability of the undercover networks and a failure to appreciate the scale of Ukrainian resistance.

That will leave Moscow scrambling to rework its political, as well as military, plans.

The FSB will be in charge of enforcing political power in cities once the military has taken them.

European intelligence officials have warned of the strategies Russia could use as it seeks to quell resistance in any cities it occupies.

"Russian officials have been considering aggressive measures to suppress likely protest and resistance," one told the BBC.

"These measures have included violent crowd-control, repressive detention of protest organisers and possibly public executions to deter Ukrainian protestors".

We've just reported that UK Home Secretary Priti Patel has announced a visa scheme to allow more Ukrainian refugees with ties to the UK to seek asylum.

Now, French authorities in Calais have released a phone number that will allow Ukrainians in Calais to get guidance from British immigration officers at the French port.

The Home Office stressed it can only offer guidance. The process of getting a visa involves an online application, then an in-person interview at the visa application centre, which is in Paris.

Image source, Reuters

A senior US defence official has just briefed journalists on how the Pentagon sees the main developments on day nine of Russia's invasion into Ukraine.

Here are the main points:

• Russia has launched more than 500 missiles since the start of the invasion and 92% of Russia's pre-staged combat power is now inside Ukraine
• However, the airspace over Ukraine continues to be contested

• The main advance of Russian forces north of Kyiv are still about 25km (16 miles) outside the city
• Russian forces are about 10km from the city centres of Chernihiv and Kharkiv

• In the south, heavy fighting is still being observed in Kherson, which has reportedly fallen to Russian control - a claim US officials were not in a position to dispute
• There is now fighting inside Mykolaiv, to the north-east of Odessa

• The US does not assess Russians are in Mariupol - but Moscow does intend to surround Mariupol from north and from the coast.

• The assault on the Zaporizhzhya nuclear power plant demonstrates the “recklessness” of the Russian invasion, but there is no radioactive leakage so far from the plant, according to US assessments

Image source, PA Media

More Ukrainian refugees can now apply to come to the UK, as a widened visa scheme has been launched.

The Home Office’s initial visa offer was restricted to immediate family, but it’s since been widened to include parents, grandparents and siblings.

Those who arrive will be given three years' leave to remain, as well as access to benefits and the right to work.

"While we want people to be able to return to their homes at the end of this diabolical invasion, giving thousands of people a route to the UK is the right thing to do," said Home Secretary Priti Patel.

Patel was speaking from Medyka, Poland, where she travelled to show “solidarity” with those helping refugees who've fled Russia’s “monstrous” invasion of Ukraine.

Of the one million people to have so far fled Ukraine, about half have gone to Poland.

Labour says many relatives of UK residents still won't qualify for a visa and "there is still no provision for people in Britain to help Ukrainian friends".

It wants the Home Office to go further and create a simple emergency visa allowing anyone fleeing the conflict to come to the UK, by lifting most usual visa conditions.

Russia has banned Facebook, according to a report by Russian state-owned news agency RIA Novosti.

It says the country's media watchdog Roskomnadzor decided to block access to the social media platform, adding there had been 26 cases of discrimination against Russian media by Facebook since October 2020, with access restricted to state-backed channels like RT and the RIA news agency.

Image source, Reuters

A Russian ambassador to the United Nations has reportedly welcomed proposals for Russian and Ukrainian ministers to hold talks in Turkey next week.

Gennady Gatilov said Turkey's idea, for foreign ministers from Ukraine and Russia to meet during a diplomatic forum in Antalya, was a good one, Russia's state-owned news agency RIA said.

As we reported earlier, a third round of talks between Ukraine and Russia is set for this weekend. There hasn't been much of a breakthrough in talks so far.

Russia's envoy to the United Nations, Vasily Nebenzya, says Ukrainian nuclear power plant and adjacent territory are being "guarded" by Russian troops.

He says the plant is working normally and background radiation levels are normal.

Image source, Reuters

Thanks for all your questionspublished at 18:00 Greenwich Mean Time 4 March 2022

18:00 GMT 4 March 2022

And that wraps up our question and answer session on the situation in Ukraine.

We've tried to answer as many of your queries as possible - huge thanks go to Professor Claire Corkhill, Frank Gardner and James Waterhouse.

We will continue to bring you the latest developments from Ukraine.

Does Nato have any strategy for Russia attacking nuclear plants in Ukraine?published at 17:57 Greenwich Mean Time 4 March 2022

17:57 GMT 4 March 2022

Frank Gardner
BBC Security Correspondent

I don’t think anyone even foresaw this, but beyond a lot of rhetoric condemning it as reckless and unacceptable, there’s not a lot the West can do, short of military intervention. This has been ruled out, as there are full-scale battles raging across Ukraine.

On the other hand, it is not in Russia’s interest to have a nuclear contamination disaster so close to its borders so this scenario may not be repeated.

Image source, Reuters

Might supplies need to be air-dropped into Kyiv?published at 17:56 Greenwich Mean Time 4 March 2022

17:56 GMT 4 March 2022

James Waterhouse
Kyiv correspondent, BBC News

Fred Williams writes in: Thank you, BBC reporters, for your bravery and reporting. If Kyiv is eventually surrounded by Russian forces, would airdrops of supplies, food and ammunition, be possible, like the Berlin airlift?

Thanks! We have an amazing team of producers, engineers, & camera operators to get us on air too.

It’s not clear yet what would happen if Kyiv is surrounded.

Negotiators from both Ukraine and Russia have agreed to create “humanitarian corridors” to let citizens escape the fighting.

It’s possible Ukrainian forces could use these temporary ceasefires to resupply, as it was agreed food and water could be delivered to cities where there’s been the heaviest fighting.

For now, supermarkets and pharmacies can stay open in cities. Stock is more limited and there are long queues though.

The distant rumbling of shells exploding is becoming more continuous as well. You become quite sensitive to the smallest changes. Occasionally a crackle of gunfire will make you jump.

Russian troops are continuing to mostly advance from the west and north, and the worry is Kyiv will find itself under a form of military chokehold, as we’ve seen with other cities.

Image source, Reuters

Russian troops have been driven out of the southern Ukrainian city of Mykolaiv, Ukrainian government official Andriy Yakobchuk says.

"But fighting is continuing in the suburbs," he adds.

Meanwhile, Ukraine's Land Forces posted footage purportedly showing its retaking the city airport and a raised Ukrainian flag.

The claims have not been independently verified.

Reports earlier on Friday said Russian troops had entered the strategically-located city with the population of about 500,000.

How could any nuclear issues in Ukraine impact the UK?published at 17:23 Greenwich Mean Time 4 March 2022

17:23 GMT 4 March 2022

Prof Claire Corkhill
Nuclear materials expert at the University of Sheffield

Victoria Urdell asked Prof Claire Corkhill: How would it affect us here in the UK if something were to happen to the nuclear plant?

We are really too far away for there to be any hazard from radioactivity being released in the event of an accident.

If an accident were to occur, it wouldn't be quite like the one that occurred at Chernobyl in 1986.

There, the graphite in the core caught fire and, because it burned for 10 days, the radioactive smoke was lifted high into the atmosphere and spread widely around Europe.

The reactors in Ukraine do not contain graphite, so are unlikely to catch fire or spread radioactivity widely.

Image source, Reuters

The UN Security Council is meeting in New York after the UK and others called for an emergency meeting following Russian shelling of a nuclear power station in Ukraine that is now under its control.

Buildings at the Zaporizhzhia nuclear power station in Ukraine - the largest in Europe - have been damaged and Ukraine says there were deaths and injuries.

The US representative, Linda Thomas-Greenfield, has been telling the meeting that Russia's actions were "reckless" and "dangerous".

"By the grace of God, the world narrowly averted a nuclear catastrophe last night. We all waited to exhale as we watched the horrific situation unfold in real time," she says.

She says Russian forces are 20 miles (32km) away from another nuclear facility and that "imminent danger" continues.

What exactly will it take for Western powers to get involved?published at 17:17 Greenwich Mean Time 4 March 2022

17:17 GMT 4 March 2022

Frank Gardner
BBC Security Correspondent

The West has made it clear it will only get involved militarily if Russia attacks a Nato country. Ukraine is not in Nato but nearby countries Poland and the Baltic states are, hence Nato has been rushing reinforcements to bolster those countries' borders.

That said, Western countries are supplying Ukraine with "defensive" equipment to help it try to repel the Russian invasion. This includes anti-aircraft and anti-tank missiles.

Some are calling for Nato to introduce a No-Fly Zone to stop Russian planes from carrying out their airstrikes on Ukrainian cities.

But Nato says it won't do that as it would entail shooting down Russian planes, and risk starting World War Three.

Why does the UN not offer monitoring forces in Ukraine?published at 17:15 Greenwich Mean Time 4 March 2022

17:15 GMT 4 March 2022

James Waterhouse
Kyiv correspondent, BBC News

Marius Crunteanua asks: why does the UN not offer monitoring forces in Ukraine? And why can’t Ukraine ask for UN peace-keeping forces to slow down events to protect the public there?

Currently Marius, the UN only carries out humanitarian and civilian operations in Ukraine. Plus, staff have had to be evacuated to safer locations because of the speed and scale of this war so far.

Ukraine’s Foreign Minister Dmytro Kuleba has said Ukraine is working on getting a UN peacekeeping mission to Ukraine, however.

“The basic way is, unfortunately, blocked,” he explained. “Because it requires an approval by the UN Security Council and Russia does not want to support such a decision.”

Ukraine is still working on this as an option.

Ukraine’s parliament has also demanded a no-fly zone to be established over Ukraine as soon as possible.

However, Western leaders have not agreed to this as they believe it would lead to a bigger conflict across Europe.

Image source, EPA

Sarah Rainsford
BBC Eastern Europe Correspondent, Kharkiv

Kharkiv is a city that’s moved underground. For more than a week now, frightened residents have been sheltering in the metro or living in their basements, hiding from the bombs and shells.

These are mostly Russian speakers - their city is 40km (25 miles) from the Russian border and they don’t understand why Russia is attacking them.

One elderly woman has spent days sleeping inside a train carriage, living off handouts and too scared to go out on the street.

She tells me people in Kharkiv respected Vladimir Putin before all this - as the president of another country - but not anymore.

She is furious. Next to her, a couple and a tiny baby lie asleep, curled up on the carriage floor.

Above ground, the entire market area has been destroyed. Volunteers pick through the ruins of a chemist shop to find medicine to give to people displaced or to the soldiers.

Opposite, a residential building with businesses on the ground floor, was also hit. All around lies the glass from blown-out windows. Locals tell us the damage is from two days ago. I could see no military target nearby.

Russia’s "high precision missiles" are hitting civilians, houses and shops.

We've heard several thuds during the day, but the shelling was lighter than it has been, so some people did venture out. One woman says "the concentration of human grief" on the metro platform is too much to bear.

At a bus stop nearby, wait groups of people clutching their pets, babies and small bags of belongings.

In tears, Svetlana tells me she's waiting for a bus, any bus, to get out - to anywhere. A shell landed 50 metres from her home last night and her nerves can no longer take it.

The Metropolitan Police in London says its war crimes team is gathering evidence in relation to alleged war crimes in Ukraine.

Any evidence may then be shared with the International Criminal Court's investigation into war crimes in Ukraine.

Commander Richard Smith, head of the Metropolitan Police's counter terrorism command, said "our war crimes team is now seeking to gather any evidence that might be present here in the UK of such crimes in Ukraine".

Detectives are appealing for anyone in the UK who may have direct evidence of war crimes in Ukraine since 21 November 2013, including any victims or witnesses.

Image source, Getty Images

What would happen if a bomb hit the nuclear power plant?published at 16:53 Greenwich Mean Time 4 March 2022

16:53 GMT 4 March 2022

Prof Claire Corkhill
Nuclear materials expert at the University of Sheffield

Maria asked Prof Corkhill: what would really happen if a fire broke out or a bomb was dropped directly at the plant or in the cooling units?

If there were a fire inside the reactor building, it would be instantly extinguished by the automatic safety systems. The reactor buildings themselves are fairly robust, so the nuclear fuel should be quite safe in there.

An explosion would only occur if there was a nuclear meltdown, which could be caused by the electricity supply to the site and the back-up generators being damaged.

If this happened to an operating nuclear power plant, then there could be an explosion like the one that happened at Fukushima (a nuclear accident in Japan in 2011).

At Zaporizhzhya, the reactors are being put into a "shutdown", which means a large-scale nuclear meltdown like that at Fukushima could not happen.

Clarification 31st August: This post was amended to clarify that the reactors being put into ‘shutdown’ would prevent a ‘large-scale’ nuclear meltdown at the plant.