"Today, March 5, from 10 am Moscow time, the Russian side declares a regime of silence and opens humanitarian corridors for the exit of civilians from Mariupol and Volnovakha," it said.

The announcement comes after Mariupol's mayor Vadim Boychenko said Saturday that the city was under "blockade" by Russian forces after days of "ruthless" attacks.

While laying siege to Mariupol for days, Russian forces have cut its electricity, food, water, heating and transportation in the depths of winter, prompting comparisons to the Nazi blockade of Leningrad in World War II.

"For now, we are looking for solutions to humanitarian problems and all possible ways to get Mariupol out of the blockade," said Boychenko, calling for a ceasefire and a humanitarian corridor for food and medicine.

Since President Vladimir Putin's army invaded on February 24, Russia has pummelled Ukrainian cities, killed hundreds of civilians and assaulted Europe's largest atomic power plant.

The invasion has drawn condemnation and severe sanctions from Western nations balancing punishment of the Kremlin with fears of a hazardous escalation.