Two Ukrainian men are suspected of collaborating with Russian intelligence to sabotage a Polish railway route before fleeing to Belarus, according to Warsaw.

Donald Tusk said the two suspects had entered Poland from Belarus and had long worked for Russia.

Donald Tusk has vowed to catch those responsible for the incident which he says could have ended in tragedy.

During a speech in parliament on Tuesday, Poland's Prime Minister Donald Tusk said the pair 'have been operating and cooperating with Russian services for a long time'.

A segment of a rail line linking Poland's capital, Warsaw, to the border with Ukraine was blown up over the weekend. Prime Minister Donald Tusk called it an "unprecedented act of sabotage".

Donald Tusk visited the site of the explosion on the Warsaw to Lublin train line – a key route into Ukraine for aid.