Poland’s prime minister has said an explosion on a railway line leading to the Ukraine border this weekend was caused by “an unprecedented act of sabotage”, and vowed to catch those responsible “regardless of who their backers are”.

Visiting the scene this morning, Donald Tusk said the damage done to the railway tracks on Sunday was deliberate and likely aimed at blowing up the train. He expressed relief there were no casualties.

Speaking later in Warsaw, after an emergency meeting of security officials, Poland’s special services minister said there was a “very high chance” that the blast was carried out on the orders of “foreign services”.