Most people trapped in the port city are sleeping underground to escape more than six days of near-constant shelling by encircling Russian forces that has cut off food, water, power and heating supplies, according to the Ukrainian authorities.

In a phone call with Turkish President Tayyip Erdogan, Putin told Erdogan he was ready for dialogue to end the fighting but that any attempt to draw out talks would fail, according to the Kremlin.

The suspension of what Moscow describes as a special operation “is only possible if Kyiv stops military operations and carries out well-known Russian demands,” the Kremlin said in a readout of the call.

The civilian death toll from hostilities across Ukraine since Moscow launched its invasion on February 24 stood at 364, including more than 20 children, the United Nations said on Sunday, adding hundreds more were injured.

The UN High Commissioner for Human Rights said most civilian casualties were caused by the use of “explosive weapons with a wide impact area, including shelling from heavy artillery and multi-launch rocket systems, and missile and air strikes.”

Russia has launched about 600 missiles so far, according to a senior US defence official.

The general staff of Ukraine’s armed forces said late on Sunday that the Russians were “beginning to accumulate resources for the storming of Kyiv”.

Moscow has repeatedly denied attacking civilian areas.

In Irpin, a town some 25 km northwest of the capital Kyiv, men, women and children trying to escape heavy fighting in the area were forced to take cover when missiles struck nearby.

Soldiers and fellow residents helped the elderly hurry to a bus filled with frightened people.

The invasion has drawn almost universal condemnation around the world, sent more than 1.5 million Ukrainians fleeing from the country, and triggered sweeping Western sanctions against Russia aimed at crippling its economy. The Biden administration said on Sunday it was exploring banning Russian oil imports.

“War is madness, please stop,” Pope Francis said in his weekly address to crowds in St Peter’s Square, adding that “rivers of blood and tears” were flowing in Ukraine’s war.

Anti-war protests took place around the world including in Russia itself, where police detained more than 4600 people, an independent protest monitoring group said. The interior ministry said 3500 demonstrators had been held, included 1700 people in Moscow and 750 in St Petersburg.

Thousands of protesters chanted “No to war!” and “Shame on you!”, according to videos posted on social media.

In the besieged city of Mariupol, authorities had said on Sunday they would make a second attempt to evacuate some of the 400,000 residents. But the ceasefire plan collapsed, as it had on Saturday, with each side blaming the other.

The International Committee of the Red Cross said the failed attempt to evacuate 200,000 people had underscored “the absence of a detailed and functioning agreement between the parties to the conflict.”

“They’re destroying us,” Mariupol mayor Vadym Boychenko told Reuters in a video call, describing the city’s plight before the latest evacuation effort failed. “They will not even give us an opportunity to count the wounded and the killed because the shelling does not stop.”

US Secretary of State Antony Blinken said the United States has seen credible reports of deliberate attacks on civilians in Ukraine, adding that Washington was documenting them to support a potential war crimes investigation.

Moscow says it has no plans to occupy Ukraine.

A huge Russian convoy north of Kyiv appears to have made limited progress in recent days, although Russia’s defence ministry released footage on Sunday showing some tracked military vehicles on the move.

The US defence official estimated that Russia has deployed about 95 per cent of the combat forces it had staged outside Ukraine.

In the capital, Ukrainian soldiers bolstered defences by digging trenches, blocking roads and liaising with civil defence units as Russian forces bombarded areas nearby.

Putin says he wants a “demilitarised”, “denazified” and neutral Ukraine, and on Saturday likened Western sanctions “to a declaration of war”.

The West, which calls Putin’s reasons for invading baseless, has expanded efforts to rearm Ukraine, sending in items from Stinger missiles to anti-tank weapons. But Washington and its NATO allies have resisted Ukraine’s plea for a no-fly zone, saying it would escalate the conflict beyond Ukraine’s borders.

Ukrainians continued to pour into Poland, Romania, Slovakia and elsewhere. The United Nations said over 1.5 million had fled in Europe’s fastest growing refugee crisis since World War Two.

Western sanctions have pushed many companies to exit investments in Russia, while some Russian banks have been shut out of a global financial payment systems, driving down the rouble and forcing Moscow to jack up interest rates.

-Reuters