Ukraine dismissed Moscow's offer to create humanitarian corridors from several bombarded cities on Monday after it emerged that exit routes would lead refugees into Russia or Belarus.
The Russian proposal of safe passage for people from Kharkiv, Kyiv, Mariupol and Sumy came after terrified Ukrainian civilians came under fire in previous failed ceasefire attempts.
Violence raged 12 days into the war, even as a third round of peace negotiations was starting on Monday and the Russian and Ukrainian foreign ministers eyed talks in Turkey later this week.
The Russian invasion has pushed more than 1.5 million people across Ukraine's borders in what the UN calls Europe's fastest growing refugee crisis since World War II, and sparked fears of a wider conflict.
International sanctions intended to punish Moscow have done little to slow the invasion, and Washington said it was now discussing a ban on Russian oil imports with Europe.
Oil prices soared to near a 14-year high on the developments while stock markets plunged.
As international pressure mounted over horrifying scenes of civilians cut down while fleeing, Moscow's defence ministry announced plans for humanitarian corridors and said a "regime of silence" had started at 0700 GMT.
But several routes led into Russia or its ally Belarus, raising questions over the safety of those who might use them.
"This is not an acceptable option," Ukrainian Deputy Prime Minister Iryna Vereshchuk said.
Russia's negotiator at the peace talks, Vladimir Medinsky, in return accused Ukraine of the "war crime" of blocking the corridors.
Expectations remained low for the talks, which were due to begin at 1400 GMT on the Belarus-Poland border, and which Medinsky said would focus on evacuation routes.
Moral cynicism
French President Emmanuel Macron, who spoke with Russian counterpart Vladimir Putin on Sunday, accused Putin of hypocrisy and cynicism over the offer.
"All this is not serious, it is moral and political cynicism, which I find intolerable," he told LCI television in an interview.
AFP journalists saw thousands of civilians early Monday fleeing the fighting via an unofficial humanitarian corridor in Irpin, a strategic suburb west of Kyiv.
"I am so happy to have managed to get out," said Olga, a 48-year-old woman leaving with her two dogs.
Children and the elderly were carried on carpets used as stretchers on the route, which leads over a makeshift bridge and then a single path secured by the army and volunteers.
Desperate people abandoned pushchairs and heavy suitcases to make sure they could get on the buses out of the war zone.
"We had no light at home, no light, 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."
A day earlier a family of two adults and two children were killed by a shell as they tried to leave the war-torn area.
"They are monsters. Irpin is at war, Irpin has not surrendered," mayor Oleksandr Markushyn said on Telegram, adding that he had seen the family killed with his own eyes.
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 Mariupol using humanitarian corridors were left stranded as the road they were directed towards was mined, the ICRC said on Monday.
Secure the skies
There was no let-up in the violence overnight into Monday, as outgunned Ukrainian forces, helped with military supplies from western countries, try to hold back Russian forces.
Air sirens sounded in cities across the country, and there was intense aerial bombardment in Ukraine's second city Kharkiv, which has endured almost non-stop fire in recent days.
"The enemy continues the offensive operation against Ukraine, focusing on the encirclement of Kyiv, Kharkiv, Chernihiv, Sumy and Mykolayiv," the General Staff of the Armed Forces of Ukraine said in a statement.
The mayor of Gostomel, the town north of Kiev that is home to a crucial military airfield, was shot dead by Russian forces along with two other people while "distributing bread to the hungry and medicine to the sick," local officials said.
Nine bodies -- five civilians and four soldiers -- were found in the rubble of Vinnytsia airport in central Ukraine after it was destroyed in a Russian missile attack on Sunday, rescue services said.
Fears meanwhile rose that the main port of Odesa, dubbed the "pearl of the Black Sea", was the next target of Russia's offensive in the south. Officials said Russia had shelled the village of Tuzly in the Odessa region from the sea, causing no injuries.
Ukraine's President Volodymyr 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?" he said in a video message.
Twelve days of fighting have killed hundreds of civilians and wounded thousands. An unending stream of people -- mostly women and children -- has poured into neighboring countries, especially Poland.
Western allies have imposed unprecedented sanctions against businesses, banks, and billionaires in a bid to choke the Russian economy and pressure Moscow to halt its assault.
Neutralisation of Ukraine
But Putin has equated global sanctions with a declaration of war, put nuclear forces on alert and warned that Kyiv is "putting in question the future of Ukrainian statehood" by continuing to resist.
Moscow has been forced to restrict sales of essential goods to limit black-market speculation, while on Sunday payment giant American Express halted operations there, a day after Visa and MasterCard announced similar steps.
Streaming giant Netflix suspended its service in Russia while social media titan TikTok halted the posting of new videos from Russia.
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.
Putin has pledged the "neutralisation" of Ukraine "either through negotiation or through war".
Sputtering diplomatic efforts to resolve the conflict continue with the foreign ministers of Ukraine, Russia and Turkey set to meet in southern Turkey on Thursday, Ankara said.
China said on Monday it was open to helping to mediate peace, but stressed that the friendship between close allies Beijing and Moscow remained "rock solid".
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.
NATO allies have so far rebuffed Ukraine's calls for a no-fly zone, with one senior US senator, Marco Rubio, saying Sunday that it could lead to "World War III" against nuclear-armed Russia.
Kyiv has urged the West to boost its military assistance, with Zelensky pleading for Russian-made planes that his pilots are trained to fly.