Two cars exploded at the gates of Saudi Arabia's huge Abqaiq oil facility today when security forces fired on suicide bombers trying to storm the world's biggest oil processing plant.
Oil Minister Ali al-Naimi said oil and gas output was unaffected by the "terrorist attempt" - the first direct strike on a Saudi oil target since al-Qaeda militants launched attacks aimed at toppling Saudi Arabia's pro-Western monarchy in 2003.
Oil prices jumped $2 a barrel on news of the attack in the world's largest oil exporter, which came a year after Saudi-born Osama bin Laden urged his supporters to hit Gulf oil targets.
Saudi security adviser Nawaf Obaid said security forces fired on three cars at the outer gates of the Abqaiq facility, 1.5 kilometres from the main entrance. One car was carrying gunmen and two others, packed with explosives, rammed the gates, he said.
It was not clear how many militants were involved in the attack, but all had been killed.
"We have yet to determine the identity of the attackers. We are currently checking DNA samples," Interior Ministry spokesman Mansour al-Turki said.
Officials say around 144 foreigners and Saudis, including security forces, and 120 militants have died in militant attacks and clashes with police since May 2003, when al-Qaeda suicide bombers struck at three Western housing compounds in Riyadh.
The next year militants bombed a Saudi security building in the capital, killed Western engineers in the Red Sea city of Yanbu, and attacked oil company and housing compounds in the Gulf city of Khobar.
Saudi officials say they have killed the most dangerous al-Qaeda leaders in the country and broken the back of their insurgency, but that al-Qaeda will remain a threat in the kingdom for years.