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 former UK Prime Minister Boris Johnson and other European security officials had passed through. The strike occurred at Yahodyn, hitting the train's engine, but no casualties were reported as all passengers had been evacuated. Johnson and European national security advisers had traveled on a different train along the same route while returning from a conference in Kyiv.