Saboteurs blew up a junction where multiple oil pipelines cross the Tigris River in northern Iraq on Tuesday, setting off a chain reaction in power generation systems that left the entire country without power, officials said.

Firefighters struggled to put out the blaze after the attack near Beiji (search), 155 miles north of Baghdad. Crude oil cascaded down the hillside into the river. Fire burned atop the water, fueled by the gushing oil.

Beiji is the point where several oil pipelines converge, said Lt. Col. Lee Morrison of the U.S. Army Corps of Engineers (search).

One of them apparently was a domestic pipeline that fed a local power plant. The explosion set off a fire that melted cables and led to the power outage, electricity officials said.

"Beiji is the chokepoint," Morrison said. "It's so easy to hit."

The 3 a.m. attack came soon after engineers had completed a two-month project to install two critical valves that had been damaged in an earlier blast.

Morrison, commander of the northern office of Task Force Shield, based in Kirkuk, said that U.S. soldiers dropped off barriers to guard the lines two days ago, but that Iraqi authorities had not yet erected them.

Iraqi oil officials have been struggling to guard the country's vast oil infrastructure, deploying thousands of oil security officers to guard the lines. Insurgents, however, have largely acted with impunity — and often inside knowledge.

"They already know it's a critical point because they've blown it up before," said Morrison, of St. Petersburg, Fla. "They obviously know the system. But it's not rocket science."

Militants waging a 16-month insurgency have attacked oil pipelines and other infrastructure as part of a campaign to destabilize the interim government of Prime Minister Ayad Allawi (search) and drive coalition forces from the country.

Allawi told the Arabic-language satellite channel Al-Arabiya on Monday that sabotage of oil pipelines had already cost the country about $2 billion in losses, with oil prices near record highs.

Iraq's Minister of Electricity Ayham al-Samarie said electricity ministry's technicians and engineers have been working to restore power for hours and 30 percent of the work has been done.

"This made the Beiji Electricity station stop for technical reasons making the whole electricity system (in Iraq) stop," al-Samarie said in a statement released by his office.

"Power will be back in the next hours," he said.