The bomb went off late Tuesday on a railroad in the province of Erzincan, damaging one of the 19 wagons of a passing freight train, the sources said.

The authorities believe the blast was the work of the outlawed Kurdistan Workers' Party (PKK), blamed for similar attacks in the past.

Two freight trains were hit by explosives attacks in the southeastern province of Mus in June and July, and five railway security guards were killed last year when a bomb ripped through a train in Bingol province, also in the southeast.

The PKK, blacklisted as a terrorist group by Turkey, the European Union and the United States, has notably stepped up its attacks this year.

The Kurdish conflict in Turkey has claimed more than 37,000 lives since 1984, when the PKK took up arms for self-rule in the mainly Kurdish southeast.