At least 51 people were killed and hundreds wounded Tuesday (Sep 3) in a Russian missile attack on the Ukrainian city of Poltava, authorities said, in one of the single deadliest strikes of the two-and-a-half-year war.

Kyiv said the strike hit a military training facility and a nearby hospital, though authorities did not say how many of the victims were military or civilians.

Ukrainian President Volodymyr Zelenskyy vowed to hold what he called "Russian scum" accountable, while rescuers worked to clear the rubble.

"According to the information available now, this Russian strike killed 51 people," Zelenskyy said in his evening address.

"The number of injured is 271. We know that there are people under the rubble of the destroyed building. Everything is being done to save as many lives as possible," Zelenskyy said.

Berlin, London and Washington all condemned the strike.

US National Security Council spokesman John Kirby said the attack was "another horrific reminder of (Russian President Vladimir) Putin's brutality", adding that the United States would send more military aid to Kyiv in the coming weeks.

British Foreign Secretary David Lammy called it a "sickening act of aggression", while German Foreign Minister Annalena Baerbock said Putin's brutality "knows no limits".