Fires blazed on a major pipeline from Iraq's northern oilfields Friday after what residents said were twin bomb attacks aimed at sabotaging exports through Turkey.
A correspondent saw two separate fires on the pipeline, 15 kilometres (nine miles) from the key refinery town of Baiji, close to the main highway between Baghdad and the northern regional capital of Mosul.
US military helicopters hovered overhead.
Residents questioned at the nearby Al-Amin coffee shop said the pipeline had been attacked by Iraqis using explosives around 8:45 pm (1645 GMT) Thursday, the same day Iraq awarded its first post-war oil export contracts.
"We heard two explosions and ran," said the coffee shop's owner, Abu Ala. "We saw fire shooting out of the pipeline in two places. Shortly afterwards two American helicopters arrived."
Customers said it had been a deliberate act of sabotage.
"Some Iraqis came and blew it up," said Kazem Ibrahim.
"It's to stop the Americans taking the oil out to Turkey," said Khidr Aziz.
Some 225 kilometres (140 miles) north of Baghdad, Baiji is home to a major refinery and power station, processing fuel from the oilfields around the northern city of Kirkuk.
Electricity generated at Baiji using Kirkuk crude is vital not just for north-central Iraq but also for the capital, where the coalition has been making desperate efforts to stem chronic post-war power cuts.
Less than an hour's drive north of Saddam Hussein's native city of Tikrit, the mainly Sunni Arab region around Baiji was considered a stronghold of his Sunni-dominated regime and several residents expressed hostility to the US-led occupation.
"The Iraqis won't change. If Saddam disappears, there will be 20 others emerging every day," said Hussein Abu Ali.
On Thursday, the US-led occupation administration awarded a raft of contracts to international oil companies to lift Iraqi crude, the first since the war.
A coalition spokesman said the contracts were for exports from the southern oilfields around Basra, and Kirkuk crude already in storage at the Turkish Mediterranean port of Ceyhan at the other end of Iraq's northern export pipeline, not new deliveries along the pipeline.
The sabotage came the same day as US troops launched a massive assault in northwestern Iraq against what commanders said was a "terrorist training camp" run by Saddam loyalists, as the coalition attempted to take the battle to an enemy in what it said was a constantly shifting guerrilla war.
US forces lost an Apache helicopter to hostile fire although both crew members were rescued by other aircraft which exchanged fire with Iraqi regulars.
Ground forces chief Lieutenant General David McKiernan declined to say exactly how many Iraqis had been killed in the operation but said it was a "very decisive, very lethal" assault.
He said the assault was a deliberate attempt to go back on the offensive after the coalition sustained a spate of casualties in deadly attacks on its troops in the Sunni tribal belt west and northwest of Baghdad.
"Coalition forces in Iraq are aggressively seeking out individuals or groups that oppose our mission.
"We are maintaining that pressure, causing him (the enemy) to react to us rather than the other way round," said McKiernan.
"We are confident that this operation set back regime loyalists and other elements trying to disrupt our operations in north central Iraq."
But the general acknowledged that his troops faced constantly changing tactics from its adversaries as they honed their ability to undermine the coalition's efforts to rebuild Iraq.
"We have seen more sophisticated techniques," McKiernan said. "As you fight the enemy, he adapts his techniques and his tactics."
"We will adapt our techniques and tactics too as we react to these forces."