A senior military source in southeast Turkey, who declined to be named, told Reuters the blast was the work of the outlawed separatist Kurdistan Workers Party (PKK).
Work to repair the pipeline, hit just after midnight, was underway and it should be operational in a few days time, said a source at state gas company Botas.
"The first results of the investigation show damage to a 30 metre (98 ft) piece of the pipeline which will need to be replaced," the Botas source told Reuters.
An energy ministry official, who declined to be named, said the blast, which he believed may have been sabotage, occurred around 13 kilometres (8 miles) inside Turkish territory.
Sabotage is common on pipelines leading into Turkey from Iran and Iraq, where Kurdish separatist militants are based.
The military source said Kurdish guerrillas had detonated explosives on the Iranian-Turkish pipeline near Dogubeyazit, close to the Iranian border.
Iran is Turkey's second biggest supplier of natural gas after Russia.
Iran accounts for more than 20 percent of Turkish natural gas imports, though supplies from Tehran are often cut in the winter months as Iran has had difficulty covering its own supply needs.
Gas was cut last winter for nearly three weeks after Turkemenistan turned off the tap to the Islamic Republic, causing a domino effect as Turkey had to stop its gas exports to Greece.
The PKK, considered a terrorist organisation by the United States, Turkey and the European Union, launched an armed campaign for an ethnic homeland in southeast Turkey in 1984.
(Reporting by Orhan Coskun in Ankara, Editing by Peter Blackburn)
