Russia on Saturday admitted using advanced hypersonic missiles for the first time in the Ukraine conflict as Kyiv's embattled leader Volodymyr Zelensky called for urgent peace talks.

Moscow also said its troops had broken Ukrainian defenses to enter the strategic southern port city of Mariupol and destroyed radio and intelligence sites just outside Odessa.

Ukrainian authorities said they had "temporarily" lost access to the Sea of Azov although Russia has effectively controlled the coastline for weeks after ringing Mariupol.

Russia said it had on Friday used the Kinzhal (Dagger) high-precision hypersonic missile, which can elude most defense systems, to destroy an arms depot in Deliatyn, a village near the border with Romania.

Moscow has never admitted using the state-of-the-art missile in combat before.

"The enemy targeted our depots" but "we have no information of the type of missile," Ukrainian air force spokesman Yuri Ignat told AFP.

"There has been damage, destruction and the detonation of munitions," he said. "They are using all the missiles in their arsenal against us."

'Time to meet, talk'

Meanwhile Ukraine's leader once again appealed for peace.

"This is the time to meet, to talk, time for renewing territorial integrity and fairness for Ukraine," Zelensky said in a Facebook video.

"Otherwise, Russia's losses will be such, that several generations will not recover."

Ukraine claimed Saturday that a Russian general had been killed by strikes on an airfield outside Kherson, just north of Crimea, saying he was the fifth top-ranking officer killed since the invasion began on February 24.

A US official said Russia's offensive remains largely stalled overall, with troops about 30 kilometers (20 miles) east of the capital Kyiv and facing heavy resistance.

Britain's defense ministry said Russia was struggling to provide its forward troops "with even basic essentials such as food and fuel" because of Ukrainian attacks on their supply lines.

But as in previous negotiations there appeared to be little progress in reaching a ceasefire, with Russian President Vladimir Putin accusing Ukraine of "numerous war crimes" during a call late Friday with French President Emmanuel Macron.

British Foreign Secretary Liz Truss accused Moscow of using the talks as a "smokescreen" as it carried out "appalling atrocities," saying she was "very skeptical" they would produce a breakthrough.

Fighting rages

As Putin's ground offensive has met with fierce resistance, Moscow has increasingly turned to indiscriminate air and long-range strikes.

Friday's attack on the arms depot was the latest strike in western Ukraine, which until a few days ago had remained relatively unscathed by Russia's push toward key cities from the north and east.

On Friday, Russian forces destroyed an aircraft repair plant near the airport of Lviv, where millions of people have fled as rockets and shelling continue to rain down on Kyiv.

In Mariupol, rescuers were still searching for hundreds of people trapped under the wreckage of a bombed theatre where over 1,000 people had been seeking shelter.

At the time of the attack, Mariupol's city council said that over 1,000 people were sheltering in the theatre's basement when it was hit on Wednesday.

There was still no information about potential fatalities, Zelensky said, but 130 people had been saved so far -- some "heavily injured."

"This is no longer Mariupol, it's hell," said resident Tamara Kavunenko, 58. "The streets are full with the bodies of civilians."

Russian forces also carried out a large-scale air strike on Mykolaiv in the south on Friday, killing dozens of young Ukrainian ensigns at their brigade headquarters.

An ensign who gave his name as Yevgen said it was home to about 200 of them.

A military spokeswoman said the final toll was still unknown, as rescuers and soldiers were still pulling out bodies as well as survivors Saturday, according to AFP reporters at the scene.

"We're still counting but it's impossible to know, given the state of the bodies," one rescuer said.

'Trapped'

More than 3.25 million refugees have fled Ukraine and countless others have sought havens in the country's west, though Putin said his forces were doing "everything possible" to avoid civilian casualties during his latest call with Macron, according to the Kremlin.

But Zelensky accused Russian forces of blocking aid around hotspot areas.

"I escaped war to reach stability, only to find myself trapped in another war," said Mazen Dammag, a Yemeni who fled his war-torn homeland nearly six years ago for Ukraine.

He and several friends hired taxis to take them from Odessa to Poland, some 1,000 kilometers north, and eventually Bremen in Germany, where he spoke with AFP by video.

Russia's ally China told US President Joe Biden on Friday that the war "in no one's interest," but showed no sign of giving in to US pressure to join Western condemnation of Russia.

Biden warned his Chinese counterpart Xi Jinping of "consequences" for any financial or military aid for Russia, a move that could turn the standoff into a global confrontation.

Putin appears undeterred by further threats or sanctions, holding a triumphalist rally in Moscow to mark eight years since Russia's seizure of Ukraine's Crimea region, saying his goal in Ukraine was "to rid these people from their suffering and genocide."

Talks stall

In a call to German Chancellor Olaf Scholz, Putin accused Ukrainian authorities of stalling talks by "putting forward more and more unrealistic proposals".

Russia wants Ukraine to disarm and disavow all Western alliances, in particular by joining NATO or seeking closer integration with the European Union -- steps that Kyiv says would turn it into a vassal state of Moscow.

Russia's top negotiator said Friday that Moscow and Kyiv had brought their positions "as close as possible" on a proposal for Ukraine to become a neutral state.

But Mikhailo Podolyak, an advisor to Zelensky taking part in the negotiations, said his country's position had not budged.