Russia bombarded Ukraine’s second-largest city with massive strikes in the early hours of Saturday, its mayor said, one night after Moscow carried out one of the war’s largest aerial assaults on Ukraine.

The United States believes that Russian President Vladimir Putin's threatened retaliation against Ukraine over its drone attack last weekend has not happened yet in earnest and is likely to be a significant,

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.

Russia launched an intense missile and drone barrage at the Ukrainian capital and three people were killed, Ukrainian officials said.

Donald Trump says Vladimir Putin told him Moscow would have to respond to Ukraine's attacks on Russian airfields. Meanwhile, the US president's NATO ambassador has demanded that countries agree to increase defence spending by 5% "now".

Russian ballistic missiles have been launched toward Ukraine from multiple directions, the Ukrainian Air Force said on Telegram Friday.

Russia's Defence Ministry said on Friday that its forces had carried out a massive and successful strike on military and military-related targets in Ukraine overnight in response to what it called Ukrainian "terrorist acts" against Russia.

A Russian rocket attack targeted the northeastern Ukrainian city of Sumy, killing at least four people and wounding 25.

A barrage of Russian strikes on Ukraine early Friday left a trail of destruction visible across several cities in the country, where some buildings and properties were destroyed. Ukrainian President Volodymyr Zelensky said Friday's strikes killed at least four people and injured dozens.