Ukrainian President Volodymyr Zelenskyy has warned of land mines left behind by Russian troops who are retreating from the outskirts of Kyiv.

Zelenskyy said in a statement on Saturday that Russian troops were slowly leaving their positions in northern Ukraine. But the president added they are laying mines across the territory and urged people not to return to those areas.

The Ukrainian government said that it had retaken more than 30 towns and villages.

Britain's defense ministry said Ukrainian troops had retaken multiple villages east of Kyiv and were moving from Irpin toward the towns of Bucha and Hostomel to the north.

Russia's defense ministry announced that the Russian forces had intensified their offensive in the regions of Kharkiv and Dnipropetrovsk, and struck armored vehicles and fuel tanks of Ukrainian troops with missiles.

Russia's state-run Tass news agency quoted presidential spokesperson Dmitry Peskov as saying that Russia had destroyed most of Ukraine's military infrastructure.

He said he hopes the goal of Russia's military operation in Ukraine will be attained as soon as possible, and hostile activities will cease. He stressed that Russia will continue fighting to liberate eastern Ukraine.

The besieged eastern city of Mariupol has been facing a serious humanitarian crisis.

Reuters reported that Ukrainian Deputy Prime Minister Iryna Vereshchuk said 4,217 residents of Mariupol had escaped from the war zone.

But more than 100,000 people are believed to be trapped in the city.