The strike was one of the deadliest for months and drew condemnation from leaders around the world, while US President Donald Trump called it a "horrible thing" and suggested Russia had "made a mistake".

Russia's defence ministry said its army launched two ballistic Iskander-M missiles at "the place of a meeting of command staff", claiming that it had killed 60 Ukrainian soldiers.

The strikes hit the centre of Sumy on Palm Sunday morning, triggering outrage in Kyiv and among its allies.

"Only completely deranged scum can do something like this," Ukrainian President Volodymyr Zelensky said.

Ukraine's emergency services said the missiles killed 34 people, including two children.

The Kremlin rejected that its army had targeted civilians or a residential area.

"Our army hits only military and military-related targets," Kremlin spokesman Dmitry Peskov told reporters when asked about the strike and Trump's comments.

The army appeared to concede that there were civilian casualties, though placed the blame on Ukraine.

"The Kyiv regime continues to use the Ukrainian population as a human shield, placing military facilities and holding events with the participation of soldiers in the centre of a densely populated city," the defence ministry said.