KYIV, Ukraine – "Around 1,300" Ukrainian troops have been killed since Russia invaded its pro-Western neighbour, the country's President Volodymyr Zelensky said on Saturday as Moscow's forces closed in on the capital Kyiv.

Zelensky made the disclosure at a media briefing, the first time Kyiv had given such a toll since the beginning of fighting. On March 2 Russia said it had lost nearly 500 soldiers, but has not updated the figure since.

The Ukrainian president claimed that Russia had lost "around 12,000 men".

It's "a ratio of one to ten, but that doesn't make me happy", he said.

The Russian army has comitted around 150,000 soldiers to the invasion of Ukraine.

Russian forces upped pressure on Kyiv Saturday, pummelling civilian areas in other Ukrainian cities, amid fresh efforts to get aid to the devastated port city of Mariupol.

Russian strikes destroyed the airport in the town of Vasylkiv on Saturday morning, about 40 kilometres (25 miles) south of Kyiv, while an oil depot was also hit and caught fire, the mayor said.

The northwest suburbs of the capital, including Irpin and Bucha, have already endured days of heavy bombardment while Russian armoured vehicles are advancing on the northeastern edge.

Ukrainian presidential adviser Mykhailo Podolyak on Friday called it a "city under siege", while Mayor Vitali Klitschko said Saturday Kyiv was reinforcing defences and stockpiling food and medicine.

The southern port city of Mariupol is facing what Ukrainian Foreign Minister Dmytro Kuleba called "the worst humanitarian catastrophe on the planet", with more than 1,500 civilians dead in 12 days.