At least three people have been killed and another 17 injured in the biggest Russian drone attack on Ukraine's Kharkiv, the city's mayor says.

A large Russian drone-and-missile attack has targeted Ukraine’s eastern city of Kharkiv, killing at least three people and injuring 21.

Ukraine’s shock drone strike on Russia’s strategic bomber fleet this week has generals and analysts taking a new look at threats to high-value United States aircraft at bases in the homeland and abroad – and the situation is worrisome.