Russia has hit Ukraine's second-largest city, Kharkiv, with a massive drone and bomber attack, killing four people and injuring nearly 60, officials say. Two people were also killed in Russian strikes on Kherson, in southern Ukraine, local authorities said.

The US president said that he discussed Ukraine's drone attack, which destroyed more than 40 Russian warplanes, with Vladimir Putin during an hour and 15 minute long phone call.

Flights were halted at Moscow’s Vnukovo and Domodedovo airports amid safety concerns following the drone attacks.