The International Atomic Energy Agency said Monday it has received reports of artillery shells damaging a nuclear research facility in Ukraine's besieged second city Kharkiv, but there was no "radiological consequence".

The Vienna-based UN body said Ukrainian authorities reported an attack took place on Sunday, adding that no increase in radiation levels had been reported at the site.

Because the site's "inventory of radioactive material is very low" and kept at a "subcritical" state, the IAEA said "the damage reported to it would not have had any radiological consequence."

The facility is part of the Kharkiv Institute of Physics and Technology, a research institute that produces radioactive material for medical and industrial applications.

Kharkiv has come under intense Russian shelling and missile attacks in recent days, as Moscow tries to step up pressure on Ukraine to surrender.

The nuclear institute itself has been at the centre of online conspiracy theories and unsubstantiated claims in Russian media that Ukraine is attempting to develop a "dirty bomb" -- a crude nuclear weapon capable of causing mass casualties.

The IAEA said this was just the latest instance of a nuclear facility becoming caught up in Russia's war on Ukraine.

"We have already had several episodes compromising safety at Ukraine's nuclear sites," said IAEA director general Rafael Mariano Grossi.

There have been reports of damage to radioactive waste disposal facilities near Kyiv and Kharkiv and Russian forces have hit the Zaporizhzhia nuclear plant, causing a fire that had to be contained.

The IAEA said the Zaporizhzhia -- Europe's largest nuclear power plant -- was now under the control of Russian forces, blocking the delivery of spare parts and medicine. 

Only two of the facility's six reactors are operating. 

Communications have also been cut with small nuclear facilities in the southern city of Mariupol -- which is surrounded by Russian forces, leaving residents without electricity or running water. 

The IAEA has urged Moscow and Kyiv to agree on a plan to safeguard nuclear facilities. 

Grossi has offered to travel to the infamous Chernobyl nuclear power plant -- site of a 1986 disaster -- where 200-plus staff have been on-site for 12 days straight. 

Ukraine escape routes

Russia said Monday it would open humanitarian corridors for civilians to flee pummelled Ukrainian cities, but Kyiv accused Moscow of making it impossible for innocent people to escape.

The latest offer brought a glimmer of hope for terrified civilians cowering under a hail of Russian shelling and mortar fire, with numerous women and children among the hundreds already killed.

Russia's defense ministry said it would open the corridors from 0700 GMT Tuesday, subject to Ukraine's approval, listing routes from Kyiv as well as the cities of Mariupol, Kharkiv and Sumy -- all of which have been under heavy attack. 

Ukraine did not initially respond to the offer, with President Volodymyr Zelensky instead accusing Moscow's troops of scuppering evacuation efforts -- mining roads and destroying buses meant to carry people to safety.

Kyiv had rejected a previous proposal for evacuation corridors from the same four cities, as many of the routes led straight into Russia or its ally Belarus.

Addressing the Security Council, the UN's top humanitarian official Martin Griffiths said civilians must be allowed to leave in the direction they wish, and safe passage be granted for vitally needed humanitarian and medical supplies.

The carnage continued on day 12 of the war, with 13 people killed in shelling on an industrial bakery in the town of Makariv and the mayor of the town of Gostomel killed while delivering bread to civilians.

According to the latest tally from the Office of the UN High Commissioner for Human Rights, which believes the real figures to be "considerably higher", 406 civilians have died since the start of Russia's assault on its ex-Soviet neighbour.

The invasion ordered by President Vladimir Putin has pushed more than 1.7 million people across Ukraine's borders in what the UN calls Europe's fastest growing refugee crisis since World War II.

International sanctions intended to punish Moscow have done little to slow the invasion, and energy-hungry Western nations are still weighing whether to ban Russian oil imports.

The conflict pushed oil prices to a near 14-year high, while gas prices also rocketed and stock markets around the world plunged.

- Abandoned pushchairs -
Outgunned Ukrainian forces have been trying to hold back Russian troops pushing up from the east and south in an attempt to encircle the capital Kyiv.

AFP journalists witnessed thousands of civilians on Monday fleeing fighting via an unofficial escape route from Irpin, a suburb west of Kyiv, towards the capital.

A day earlier eight people died there in shelling, Ukrainian officials said. Images of the killing of one family of four shocked the world.

"There was firing on all sides when we were on the road, but we got across," Tetyana, 51, told AFP after crossing icy water on a rickety plank, over which thousands have fled Russian bombardment.

"I told myself that if I was killed on the spot, so be it, but if I'm wounded, I'll have to crawl," she said.

Children and the elderly were carried on carpets used as stretchers on the route, which leads over the makeshift bridge and along a single path secured by the army and volunteers.

Desperate people abandoned pushchairs and heavy suitcases to cram on buses out of the war zone.

"We had no light at home, no water, we just sat in the basement," Inna Scherbanyova, 54, an economist from Irpin, told AFP.

"Explosions were constantly going off... Near our house there are cars, there were dead people in one of them... very scary."

One Ukrainian paratrooper told of "hand-to-hand" combat in Irpin, saying "we are trying to push (Russian soldiers) out, but I don't know if we'll be fully able to do it".

Two recent attempts to allow some 200,000 civilians to leave the besieged Azov Sea port of Mariupol have also ended in disaster.

Refugees trying to escape the city using agreed escape routes were left stranded as the road they were directed towards was mined, the ICRC said on Monday. 

On the European front, meanwhile, EU foreign policy chief Josep Borrell said the conflict could drive five million Ukrainian refugees into the roads "if the indiscriminate bombardments of cities continues".

- Oil exports dilemma -
Ukraine's Zelensky renewed calls for the West to boycott Russian exports, particularly oil, and to impose a no-fly zone to stop the carnage.

"How many more deaths and losses must it take to secure the skies over Ukraine?" the president said in a video message.

While NATO countries have pumped weapons into Ukraine, they have so far rebuffed Ukraine's calls for a no-fly zone, fearing a widening war against nuclear-armed Russia.

Western allies have instead imposed unprecedented sanctions against businesses, banks and billionaires in a bid to choke the Russian economy and pressure Moscow to halt its assault.

But the leaders of Germany, Britain and the Netherlands warned Monday against a ban on Russian oil, saying it could put Europe's energy security at risk.

US President Joe Biden's spokeswoman said no decision had been taken, while Russian Deputy Prime Minister Alexander Novak warned any oil ban would have "catastrophic consequences" on prices.

Meanwhile, Moscow has been forced to restrict sales of essential goods to limit black market speculation, while a stream of foreign companies halted business in Russia.

While Japanese casualwear giant Uniqlo defended its decision to stay, calling clothing "a necessity of life", US jeans brand Levi's became the latest to join the exodus.

"I came to buy my favourite brands one last time," 19-year-old student Filippova told AFP at a mall in Moscow.

Putin has equated sanctions with a declaration of war and put nuclear forces on alert, pledging the "neutralisation" of Ukraine "either through negotiation or through war".

Despite harsh punishments for those voicing dissent, protests in Russia against the Ukraine invasion have continued, with more than 10,000 people arrested since it began.

The International Court of Justice meanwhile heard Ukraine's appeal for it to order Russia to halt the fighting, but Moscow declined to attend the sitting of the UN's top court, in The Hague.

Latest developments

- Russian evacuation offer rejected -

Ukraine rejects a Kremlin offer to open escape routes for civilians trapped by the fighting in the cities of Kharkiv, Kyiv, Mariupol and Sumy because several of the routes lead to Russia or its ally Belarus.

Moscow says the proposal was based on a request from French President Emmanuel Macron, denied by Macron, and accuses Ukraine of blocking civilians from leaving, which it calls a "war crime".

- Shelled while fleeing -
Russia steps up its shelling of cities, including the town of Gostomel near Kyiv, Kharkiv in the east, Sumy in the northeast, Chernihiv in the north and Mykolayiv in the southwest.

Ukraine's President Volodymr Zelensky accuses Russian troops of the "deliberate murder" of civilians after a family with two children was killed by shelling while trying to flee the town of Irpin.

Tens of thousands are still trapped without water or power in the southern port of Mariupol after two failed evacuation attempts.

- Bakery hit -
At least 13 people are killed by shelling at an industrial bakery in Makariv, around 50 kilometres west of Kyiv, Ukrainian rescue services say.

- More talks -
A third round of talks between Ukrainian and Russian delegations gets underway on the Belarus-Poland border to discuss humanitarian corridors.

Turkey announces it will host Russia's and Ukraine's foreign ministers for talks Thursday.

- EU to consider membership bids -
EU members agree to start the lengthy process of examining membership bids submitted by Ukraine, Georgia and Moldova in the wake of Russia's invasion of its neighbour.

- Rock-solid friendship -
China's foreign minister says the friendship between Beijing and Moscow is "rock solid" despite the Russian invasion and offers to help mediate.

- Oil, gas prices rocket - 
Oil prices hit a near 14-year high and European and UK natural gas prices reach record levels after the United States proposes an embargo on Russian oil imports.

The leaders of Germany, Britain and the Netherlands warn against such a ban, however, saying it could put Europe's energy security at risk.

- Debts paid in rubles -
Russia says it will allow Russian companies and individuals to repay debts to creditors in "hostile" nations, including the US, EU, Britain, Canada and Japan in the battered national currency, the ruble.

- Russia snubs international court -
Russia snubs a hearing at the International Court of Justice in The Hague at which Ukraine seeks an immediate order to halt the conflict.

- Russians need clothes: Uniqlo -
Japanese casualwear giant Uniqlo defends a decision to keep Russian stores open even as rivals Zara and H&M suspend operations in the country over the invasion of Ukraine.

"Clothing is a necessity of life," says Tadashi Yanai, president of Uniqlo operator Fast Retailing.

- Visas row -
British Prime Minister Boris Johnson defends his government from accusations of being unwelcoming to Ukrainian refugees, saying it has granted only about 50 visas so far because of the need to screen all newcomers for security reasons.

- 1.7 million refugees -
The UN says 1.7 million people have fled Ukraine, making it the fastest-growing refugee crisis since World War II.