Scott Sibley, believed to be 36, has been named as the Briton who died.

It is thought the pair could have been fighting against Russian troops as volunteers in support of Ukraine's military, although this has not been confirmed.

British nationals, and other foreigners, have also travelled to Ukraine to take part in humanitarian assistance.

A post on the Logistics Support Squadron Facebook page described him as a "former serving soldier" of the squadron and said he had "showed Commando spirit until the end".

Mr Sibley is a veteran of the British armed forces, it is understood.

The Foreign, Commonwealth and Development Office (FCDO) did not provide any details on what the men had been doing in Ukraine.