U.S. President Joe Biden cast doubt on Russia's signal that it may scale down its war aims to concentrate on eastern Ukraine, as two Russian missile strikes slammed into the west of the country on Saturday, wounding five.
After failing to break Kyiv's ferocious resistance in a month of fighting and deadly attacks on civilians, the Russian army in a surprise announcement said it would focus on "the main goal — the liberation of Donbas."
But Biden said he was "not sure" that Moscow has indeed changed strategy, as he branded Russian President Vladimir Putin a "butcher" while meeting Ukrainian refugees in Poland.
The U.S. leader's assessment came as two missiles struck a fuel depot in western Ukraine's Lviv, a rare attack on a city just 70 kilometers (45 miles) from the Polish border that has escaped serious fighting since Russian troops invaded last month.
At least five people were wounded, regional governor Maksym Kozytsky said, as AFP journalists in the city center saw plumes of thick black smoke.
Putin sent troops into Ukraine on February 24, vowing to destroy the country's military and topple pro-Western President Volodymyr Zelensky.
But his army has made little progress on capturing key cities, and its attacks that have hit hospitals, residential buildings and schools have become more deadly.
Biden, who has been leading efforts among Western allies to press Putin to end his invasion of Ukraine, has blasted Putin as a "war criminal" over the assaults on civilians.
The Kremlin hit back at Biden's description of Putin as a "butcher", saying "a state leader must remain sober-minded."
"Such personal insults are narrowing down the window of opportunity for our bilateral relations under the current (U.S.) administration. One should be aware of this," said Kremlin spokesman Dmitry Peskov, in remarks carried by state news agency TASS.
Biden, who is on a two-day visit to Poland after holding a series of summits in Brussels with Western allies, earlier met Ukraine's Foreign Minister Dmytro Kuleba and Defense Minister Oleksii Reznikov in Warsaw in an emphatic show of support for Kyiv.
Both ministers had made a rare trip out of Ukraine for the face-to-face talks, in a possible sign of growing confidence in their fightback against Russian forces.
The talks discussed Washington's "unwavering commitment to Ukraine's sovereignty and territorial integrity," State Department spokesperson Ned Price told reporters.
Biden, who later met Polish President Andrzej Duda, also stressed the "sacred commitment" to NATO's collective defense, in a clear reassurance to Ukraine's neighbors rattled by the conflict.
"You can count on that... for your freedom and ours," he told Duda.
Speaking after visiting Ukrainian refugees later Saturday, Biden said he had been asked by children to pray for their male relatives fighting in Ukraine.
"I remember what it's like when you have someone in a war zone and every morning you get up and you wonder... you are praying you don't get that phone call," said Biden, whose son Beau served in Iraq before dying of a brain tumor.
On the frontlines, Russia's far-bigger military continued to combat determined Ukrainian defenders who are using Western-supplied weapons — from near the capital Kyiv to Kharkiv, the Donbas region and the devastated southern port city of Mariupol.
A humanitarian convoy leaving Mariupol, including ambulances carrying wounded children, was being held up at Russian checkpoints, a Ukrainian official said.
A buildup of several kilometers had formed close to Vassylivka, in the region of Zaporizhzhia where the convoy was headed, said Lyudmyla Denisova, in charge of human rights in Ukraine.
"The ambulances carrying wounded children are also queueing. The people have been deprived of water and food for two days," she wrote on Telegram, blasting Russian troops for "creating obstacles".
Authorities have said they fear some 300 civilians in Mariupol may have died in a Russian air strike on a theatre being used as a bomb shelter last week.
Russian forces hammering Mariupol's out-gunned resistance consider the city a lynchpin in their attempt to create a land corridor between the Crimea region, which Moscow seized in 2014, and the Donbas.
One Mariupol resident who managed to escape the city, Oksana Vynokurova, described leaving behind complete devastation.
"I have lost all my family. I have lost my house. I am desperate," the 33-year-old told AFP after reaching Lviv by train.
"My mum is dead. I left my mother in the yard like a dog, because everybody's shooting."
In Kharkiv, where local authorities reported 44 artillery strikes and 140 rocket assaults in a single day, residents were resigned to the incessant bombardments.
Anna Kolinichenko, who lives in a three-room flat with her sister and brother-in-law, said they don't even bother to head down to the cellar when the sirens go off.
"If a bomb drops, we're going to die anyway," she said. "We are getting a little used to explosions".
Russian forces have taken control of Slavutych, the town where workers at the Chernobyl nuclear plant live, briefly detaining the mayor, regional Ukrainian authorities said.
Residents of the town protested, prompting the invading forces to fire shots in the air and lob stun grenades into the crowd.
Kyiv said it was shortening a planned 35-hour curfew to just Saturday 8:00 pm to Sunday 7:00 am, as Britain's defense ministry said Ukrainian counter-attacks were underway near the capital.
Ukrainian forces were also attempting to recapture Kherson, the only major city held by Russian invasion troops, a Pentagon official said.
Russia's army had been predicted by some to roll across Ukraine with little resistance, but it had greatly underestimated Ukrainian determination.
Putin's military has also exhibited poor discipline and morale, faulty equipment and tactics, as well as brutality toward civilians, Western analysts say.
Amid heavy censorship, Russian authorities Friday gave only their second official military death toll since the start of the invasion, at 1,351.
This is far below Western estimates, with one senior NATO official saying between 7,000 and 15,000 Russian soldiers have died.
Sergei Rudskoi, a senior Russian general, suggested the time had come for a considerably reduced "main goal" of controlling Donbas, an eastern region already partly held by Russian proxies.
Rudskoi said Ukraine's military has been severely degraded and that Russia hadn't seized cities to "prevent destruction and minimize losses among personnel and civilians."
While diplomatic efforts have so far done little to stop Russia, Zelensky pressed on with his relentless bid to rally world leaders to his side.
This time taking his message to the Doha Forum meeting in Qatar's capital, he accused Russia of fuelling a dangerous arms race by "bragging" about its nuclear stocks.
He also urged Qatar to help stop Moscow from deploying energy as a weapon.
"I ask you to increase the output of energy to ensure that everyone in Russia understands that no one can use energy as a weapon to blackmail the world," Zelensky said.