Watch: Why a Russian strike on train near Ukraine-Poland border could mark an escalation

A Russian drone struck a train near the Ukraine-Poland border shortly after the former UK Prime Minister Boris Johnson and top European security officials had passed through.

No casualties were reported after the strike at Yahodyn, which hit the train's engine. All the passengers had been evacuated, Ukrainian authorities said.

Johnson and other European national security advisers, including the UK's Jonathan Powell, had passed along the same line on a different train on their way back from a conference in Kyiv.

BBC's James Landale explains why the incident could signal an escalation in Russia's war against Ukraine.