The attack on Friday, which killed at least four people nationwide, came two days after Russia vowed retaliation for an audacious drone assault on its strategic bomber bases.

Officials say Ukraine was under an ongoing Russian ballistic missile and drone attack early Friday that wounded at least three people.

Russia launched large-scale drone and missile strikes on Ukraine's capital and other parts of the country early on Friday, local officials said. At least four people were killed in Kyiv and at least 20 have been injured, the city's mayor Vitaliy Klitschko said.