BAGHDAD, Iraq — Insurgents bombed an oil pipeline in southern Iraq, setting off a huge blaze and slashing daily Iraqi oil exports by about 25 percent, or 450,000 barrels per day, an official said Monday.

Insurgents have often attacked the much smaller northern pipeline to Turkey but attacks against Iraq's southern oil facilities, which account for almost 90 percent of the country's exports, have been rare.

Militants set off the bomb Saturday under the Faw oil pipeline, some 35 miles south of the main southern city of Basra, said an engineer at Iraq's Southern Oil Company, speaking on condition of anonymity.

Firefighters have been fighting the blaze since it began, said Jabber Luyaibi, director general of Iraq's Southern Oil Company.

Luyaibi said the blast damaged a 18-foot section of one of two pipelines that run from Basra to the Faw peninsula on the Gulf. The pipelines have a capacity of 2 million barrels per day - larger than Iraq's current exports.

Luyaibi said that engineers were able to move oil from the damaged pipeline to the second pipeline.

But an official for the State Oil Marketing Pipeline later told Dow Jones that the damage was still considerable and that the second pipeline's capacity was too small to carry all of the additional exports. He told Dow Jones that exports had fallen to 1.2 million barrels a day following the blast.

The official, who spoke on condition of anonymity, told Dow Jones that repairs to the pipeline should take another 48 hours.

Dan Senor, a spokesman for the coalition, confirmed that there was a bombing but gave no details, saying that to do so might help the insurgents.

"Any information we provide about success or failure of those attacks, particular the details, can be used as a basis for information in future attacks," Senor said at a press conference.

Paul Horsnell, head of energy research at Barclays Capital in London, said the blast is likely to cause only a temporary disruption of exports.

But he said the significance of the attack is that "quite clearly, now the southern infrastructure is a target."

Iraq exports some 1.65 million barrels per day from the south and another 200,000 barrels per day from the north through Turkey.

In late April, suicide bombers in boats attacked Iraqi pumping stations in the Gulf, briefly disrupting Iraqi oil exports.