Russian soldiers walk along a street in Mariupol. AFP

Russia told Ukrainian forces fighting in the besieged city of Mariupol to lay down their arms starting 6am Moscow time (0300 GMT) on Sunday to save their lives.

Thirty minutes after the ultimatum, there were no immediate reports of activity in the strategic southeastern port. Air raid sirens sounded across the country, a regular occurrence, but there were no reports of any strikes.

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Russia's Defence Ministry said its troops had cleared the urban area of Mariupol and only a small contingent of Ukrainian fighters remained inside a steelworks in the city on Saturday.

Meanwhile, Ukraine's President Volodymyr Zelensky said the situation in Mariupol is "inhuman" and called on the West to immediately provide heavy weapons, as Russia claimed it was in control of almost all of the strategic port city and urged its last defenders to surrender.

Local residents walk past a destroyed part of the metallurgical plant in Mariupol, Ukraine, on Saturday. AP

Moscow said Ukrainian forces in the city must lay down their arms by Sunday, after weeks of relative calm in the capital Kyiv were brought to an end by renewed Russian airstrikes.

Moscow's claim to have all but taken control of Mariupol, scene of the war's heaviest fighting and worst humanitarian catastrophe, could not be independently verified. It would be the first major city to have fallen to Russian forces since the Feb. 24 invasion.

"Taking into account the catastrophic situation that has developed at the Azovstal metallurgical plant, as well as being guided by purely humane principles, the Russian Armed Forces offer the militants of nationalist battalions and foreign mercenaries from 06:00 (Moscow time) on April 17, 2022, to stop any hostilities and lay down their arms," the defence ministry said in a statement.

A Russian military convoy moves on a highway near Mariupol, Ukraine, on Saturday. AP

"All who lay down their arms are guaranteed that their lives will be spared," it said, adding that the defenders could leave the plant by 10 a.m. without arms or ammunition.

There was no immediate response from Kyiv.

"The situation is very difficult" in Mariupol,Zelensky told the Ukrainska Pravda news portal. "Our soldiers are blocked, the wounded are blocked. There is a humanitarian crisis... Nevertheless, the guys are defending themselves."

As Moscow launched long-range missile attacks across the country following the sinking of its Black Sea flagship, Moscow said its warplanes had struck a tank repair factory in Kyiv on Saturday. An explosion was heard and smoke rose over the southeastern Darnytskyi district. The mayor said at least one person was killed and medics were fighting to save others.

The gutted remains of vehicles lie at the Illich Iron & Steel Works Metallurgical Plant in Mariupol. AP

The Ukrainian military said Russian warplanes that took off from Belarus had fired missiles at the Lviv region near the Polish border and four cruise missiles were shot down by Ukrainian air defences.

The western city, relatively unscathed so far, has served as a haven for refugees and international aid agencies.