Several fire service teams worked through the night to quell the flames, while bomb disposal experts also defused another powerful device in the same area, a local security source told AFP.

The blast that ripped through the pipeline in the Mardin region near the village of Midyat on Tuesday killed two civilians who had been driving past in their car.

The authorities suspect the PKK carried out the attack, but the group has not claimed responsibility, although they have attacked the pipeline in the region several times, including last month.

The 970-kilometre (600-mile) pipeline carries crude oil from Kirkuk in northern Iraq to Ceyhan, where it is loaded onto tankers.

The PKK, listed as a terrorist group by Turkey and much of the international community, took up arms for self-rule in the Kurdish-majority southeast in 1984, sparking a conflict that has claimed around 45,000 lives.

It has significantly stepped up attacks since its jailed leader Abdullah Ocalan declared in May he was abandoning efforts to seek dialogue with Ankara.