"There are few things more depraved than targeting the vulnerable and defenceless," Johnson tweeted.

"The UK is exploring more support for Ukraine to defend against airstrikes and we will hold Putin to account for his terrible crimes," he said, after a local official said the strike had wounded 17 hospital staff.

In parliament earlier, Defence Secretary Ben Wallace said the UK was preparing to send more portable missile systems to help Ukrainian forces destroy Russian tanks and aircraft.

But he denied Britain risked escalating the conflict, insisting the weaponry was "defensive".