The main oil export pipeline linking Iraq and Turkey, halted since the US invasion, was hit by fire and explosions caused by a gas leak, US authorities in Iraq said.
Turkey said investigations were under way to establish whether sabotage was to blame for the blast in the Iraqi section of the pipeline in northern Iraq last night.
The Turkish state-run news agency Anatolian said its correspondent in Iraq had reported another explosion this afternoon around 50 km (30 miles) from the previous blast. It gave no explanation for the latest explosion.
US military spokesmen said earlier there was no sign that sabotage had caused Thursday's explosions. Occupying U.S. forces have accused saboteurs for undermining their efforts to restore the oil industry.
"There is no evidence that there was any hostile intent. US and Iraqi engineers are assessing the extent of the damage," a spokesman said.
Turkish Foreign Minister Abdullah Gul, in an initial response, said there was sabotage and that an investigation was under way. But a Foreign Ministry official said later the Ankara government had not yet received conclusive evidence on whether the blast was caused by a leak or sabotage.
Yesterday Iraq concluded its first oil sales since the war, awarding a tender to sell 10 million barrels of crude held in storage.
A steady flow of oil through the pipeline was expected to begin later this month. It is still not clear whether oil production in northern Iraq was affected.
Iraq is struggling to revive its oil industry, which was battered by years of wars and United Nations sanctions under the rule of Saddam Hussein.