Russian forces upped pressure on Kyiv Saturday, pummelling civilian areas in other Ukrainian cities, amid fresh efforts to get aid to the devastated port city of Mariupol.
Russian strikes destroyed the airport in the town of Vasylkiv on Saturday morning, about 40 kilometres (25 miles) south of Kyiv, while an oil depot was also hit and caught fire, the mayor said.
The northwest suburbs of the capital, including Irpin and Bucha, have already endured days of heavy bombardment while Russian armoured vehicles are advancing on the northeastern edge.
Ukrainian presidential adviser Mykhailo Podolyak on Friday called it a "city under siege", while Mayor Vitali Klitschko said Saturday Kyiv was reinforcing defences and stockpiling food and medicine.
Buses were continuing to bring refugees into the city from the hard-hit suburbs Klitschko said in a video message, adding: "We will not give up."
Other cities have already fallen or been surrounded following Russia's invasion of its neighbour on February 24, with civilians targeted in what the United Nations warned could amount to war crimes.
The southern port city of Mariupol is facing what Ukrainian Foreign Minister Dmytro Kuleba called "the worst humanitarian catastrophe on the planet", with more than 1,500 civilians dead in 12 days.
Kyiv said on Saturday that Russian forces shelled a mosque in Mariupol where 80 civilians, including Turkish citizens, had taken shelter.
However, this was denied by Ismail Hacioglu of the local mosque association, who told Turkish television the area was under fire but the mosque was not hit.
A humanitarian convoy carrying food and medicine for around 400,000 residents in Mariupol on Saturday left Zaporizhzhia, to the north east, city officials said, with buses to bring civilians back.
Clergy from the Orthodox Church would accompany the convoy, they said, after Ukraine's President Volodymyr Zelensky accused Russia of targeting previous similar efforts.
Meanwhile an AFP reporter in the southern city of Mykolaiv said a hospital in the northern district of Ingulski came under fire, while heating is out in the area, forcing many residents to flee.
"They shot at the civilian areas, without any military objective," said the hospital's head, Dmytro Lagochev, adding: "There's a hospital here, an orphanage and an ophthalmological clinic."
Mykolaiv, which lies on the road to the strategic port city of Odessa, has been under attack for days.
Pay the price
The United Nations estimates that 2.5 million people had fled Ukraine since the invasion, most of them to Poland, in the worst refugee crisis since World War II.
As Russia widens its bombardment and talks between Moscow and Kyiv seemingly go nowhere, Zelensky's pleas for NATO to intervene have grown increasingly desperate.
Washington and its EU allies have sent funds and military aid to Ukraine, taken action against its economy and oligarchs, and a cultural and sporting boycott has squeezed Russia's soft power.
But US President Joe Biden on Friday again ruled out direct action against nuclear-armed Russia, warning that it would lead to "World War III".
Instead, Washington added more layers of sanctions to those already crippling Russia's economy, this time ending normal trade relations and announcing a ban on signature Russian goods vodka, seafood and diamonds.
The United States and the European Union also suspended the export of their luxury goods to Russia.
Russian President Vladimir "Putin must pay the price," Biden said from the White House.
'Cinders in his lungs'
The situation in Mariupol remains "desperate", according to Doctors Without Borders, with no water or heating -- and food supplies dwindling.
"Hundreds of thousands of people... are for all intents and purposes besieged," Stephen Cornish, one of those heading the medical charity's Ukraine operation, told AFP in an interview.
"Sieges are a medieval practice that have been outlawed by the modern rules of war for good reason."
The central city of Dnipro, an industrial hub of one million inhabitants, saw its reputation as a relatively safe haven shattered when three missiles hit civilian buildings Friday.
Images of its charred or destroyed buildings -- including a kindergarten with windows blown out -- now join those from Kharkiv and Mariupol in illustrating the brutality of the conflict.
In Kharkiv, in the east, doctors at a hospital described spending two days pumping ash from the stomach of an eight-year-old child whose home was struck by a Russian missile.
"He still has cinders in his lungs," Dima Kasyanov's doctor told AFP.
The attacks on civilians prompted a new flurry of warnings on Friday that Russia is committing war crimes -- although the Kremlin has denied it attacked Ukraine, saying it launched a "special military operation" to stop a direct threat.
"We are really heading towards an unimaginable tragedy," warned Cornish, of Doctors Without Borders, insisting that "there is still time to avoid it, and we must see it avoided".
Foreign combatants
In the latest of his regular video messages, Zelensky appealed to Russian mothers to prevent their sons from being sent to war, and said Moscow was suffering "enormous losses".
US estimates put the number of Russian fatalities at 2,000 to 4,000 while Moscow's only official toll, announced last week, said 498 Russian troops had been killed.
Foreign combatants have already entered the Ukrainian conflict on both sides, and on Friday, the Kremlin ramped up efforts to bring in reinforcements, particularly from Syria.
On Saturday, Zelensky urged Ukrainians to "give everything" to defend the country.
"This is a war for our independence. Not just for the state, but for everything Ukrainian that was before, is now and will be," he said.
'Serious diplomacy'
In the Russian-held city of Melitopol, Zelensky said 2,000 people protested against the kidnapping Friday of the mayor.
He called on the leaders of France and Germany to help secure Ivan Fedorov's release, which he said opened a "new stage of terror".
French President Emmanuel Macron held new talks with Putin about the conflict Saturday.
Numerous efforts are underway to find a diplomatic solution to the crisis, with Turkey on Thursday hosting the first talks between the Russian and Ukrainian foreign ministers since war erupted.
There was no breakthrough but Putin said Friday there were some "positive shifts" and that negotiations were being held "almost daily".
US Vice President Kamala Harris, speaking in Bucharest, said the Russian leader had shown "no sign of engaging in serious diplomacy".
At the United Nations, Western countries accused Russia of spreading "wild" conspiracy theories after Moscow's envoy told diplomats that America and Ukraine had researched using bats to conduct biological warfare.
The US envoy said Russia had made the claims as part of a "false flag effort" for using chemical weapons of its own in Ukraine.
Biden warned Russia would pay a "severe price" if it used chemical weapons -- but added: "We will not fight a war against Russia in Ukraine".