LVIV/KYIV, Ukraine (Reuters) -- Fighting stopped about 200,000 people from evacuating the besieged Ukrainian city of Mariupol for a second day in a row on Sunday, as Russian President Vladimir Putin vowed to press ahead with his invasion unless Kyiv surrendered.
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 said 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 Putin-Erdogan call.
The civilian death toll from hostilities across Ukraine since Moscow launched its invasion on Feb. 24 stood at 364, including more than 20 children, the United Nations said on Sunday, adding that hundreds more were injured.
The U.N. 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 airstrikes."
Russia has launched about 600 missiles so far, according to a senior U.S. defense official.
The general staff of Ukraine's armed forces said 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 (16 miles) 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, according to Reuters witnesses.
Soldiers and fellow residents helped the elderly hurry to a bus filled with frightened people, some cowering as they waited to be driven to safety.
The invasion has drawn widespread 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 imports of Russian oil, despite concerns the move would drive prices even higher.
Oil prices have soared to their highest levels since 2008 and jumped 10% in early Asian trade on Monday. Russia provides 7% of global supply.
"War is madness, please stop," Pope Francis said in his weekly address to crowds in St Peter's Square, adding "rivers of blood and tears" were flowing in Ukraine's war.
Russian media said Putin also spoke by phone for almost two hours with French President Emmanuel Macron. Macron told Putin he was concerned about a possible amphibious attack on Ukraine's historic port city of Odesa, Macron's office said.
The United States does not believe such an attack is imminent, the senior U.S. defense official said, speaking on condition of anonymity.
Anti-war protests took place around the world, including in Russia itself, where police detained more than 4,600 people, an independent protest monitoring group said.
The interior ministry said 3,500 demonstrators had been held, including 1,700 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 by opposition activists and bloggers. Reuters was unable to independently verify the footage and photographs.
Demonstrations also took place in Western capitals as well as in India and Kazakhstan, after jailed Kremlin critic Alexei Navalny called for worldwide protests against the war.
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 cease-fire plan collapsed, as it had on Saturday, with each side blaming the other.
"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."
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.
The U.S. defense official estimated Russia has deployed about 95% of the combat forces it had staged outside Ukraine.
In the capital, Ukrainian soldiers bolstered defenses by digging trenches, blocking roads and liaising with civil defense units as Russian forces bombarded areas nearby.
Ukrainian President Volodymyr Zelenskyy said Russian rockets had destroyed the civilian airport of the central-western region capital of Vinnytsia. Troops who committed atrocities against civilians would ultimately face punishment, he said.
"For you there will be no peaceful place on this earth, except for the grave," he said in a televised evening address.
Russian forces opened fire at a protest against their occupation of the southern Ukrainian city of Nova Kakhovka on Sunday, wounding five people, Ukrainian news agency Interfax Ukraine said, citing eyewitnesses.
Kyiv renewed its appeal to the West to toughen sanctions and also requested more weapons, including Russian-made planes.
Speaking on a trip to neighboring Moldova, Blinken said Washington was considering how it could backfill aircraft for Poland if Warsaw decided to supply its warplanes to Ukraine.
Putin says he wants a "demilitarized," "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 II.
Western sanctions have pushed many companies to exit investments in Russia, while some Russian banks have been shut out of a global financial payment system, driving down the ruble and forcing Moscow to jack up interest rates.
On Sunday, more companies cut ties with Russia: American Express Co AXP.N, Netflix Inc. NFLX.O, accounting giants KPMG and PwC, and video sharing app TikTok.
But Chinese companies so far are staying put.
Ukraine's military said more than 11,000 Russian troops had been killed so far and 88 Russian aircraft shot down since the start of the invasion. Reuters could not corroborate the claim. Russia has not given regular updates on its death toll.
Tass news agency cited Russian defense ministry spokesman Igor Konashenkov as saying virtually the entire Ukrainian air force had been destroyed. In the last 36 hours alone, he said, Ukraine had lost 11 combat aircraft and two helicopters. Reuters had no way of corroborating the claim.