President Volodymyr Zelensky called on Saturday for comprehensive peace talks with Moscow to stop its invasion of Ukraine, saying it would otherwise take Russia "several generations" to recover from its losses in the war.

Since Russian President Vladimir Putin launched the assault on Feb. 24, Russian forces have taken heavy losses and their advance has largely stalled, with long columns of troops that bore down on Kyiv halted at its suburbs.

However they have laid siege to cities, blasting urban areas to rubble, and in recent days have intensified missile attacks on scattered targets in western Ukraine, away from the main battlefields in the north and east of the country.

On Saturday Russia's defence ministry said it had destroyed a large underground depot for missiles and aircraft ammunition in the western Ivano-Frankivsk region using hypersonic weapons, missiles that can travel at five times the speed of sound or faster.

Missiles also destroyed Ukrainian military radio and reconnaissance centres near the port of Odessa, the Interfax news agency quoted the ministry as saying.

Reuters was unable to independently verify the reports. Zelensky's office did not immediately respond to a request for comment.

Ukrainian authorities said on Saturday they have not seen any significant shifts over the past 24 hours in front line areas, noting cities of Mariupol, Mykolaiv and Kherson in the south and Izyum in the east saw particularly heavy fighting.

More than 3.3 million refugees have already fled Ukraine through its western border, with 2 more million displaced inside the country. Efforts to evacuate civilians from cities under siege through "humanitarian corridors" continued.

Ukrainian authorities said they hoped to open 10 such corridors on Saturday.

Unprecedented Western sanctions aimed at crippling Russia's economy and starving its war machine have yet to halt what Putin calls a "special operation" to disarm its neighbour and purge it of "Nazis". Kyiv and its allies have called this a baseless pretext for war.

Ukraine's defence ministry acknowledged on Friday it had "temporarily" lost access to the Azov Sea, a strategic link with the Black Sea, after Russia said it was "tightening the noose" around the besieged southern port of Mariupol.

Hundreds of thousands have been trapped there for over two weeks with electricity, water and heat supplies cut off. Its Soviet-era apartment blocks blasted into burned out shells and covered-up uncollected bodies amid the rubble a common sight. Local officials say fighting has reached the city centre while heavy shelling keeps humanitarian aid from getting in. 

Rescue workers were still searching for survivors of a Mariupol theatre that local authorities say was flattened by Russian air strikes on Wednesday. Russia denies hitting the theatre and says it is not targeting civilians.