Suicide bombers in explosives-laden cars today tried to attack an oil-processing facility that handles about two-thirds of Saudi Arabia's petroleum output.
They were stopped when guards opened fire on them, causing the cars to explode, officials said.
The Saudi oil minister said the blast "did not affect operations" at the Abqaiq facility, denying an earlier report on Al-Arabiya television that the flow of oil was halted briefly after a pipeline was damaged.
The price of oil jumped by more than $1.20 on world markets as they heard of the attack. The April delivery price of Nymex sweet light crude, the US benchmark, rose $1.26 to $61.80.
The European benchmark, Brent crude, leaped $1.21 to $61.75 for April delivery.
It was the first attack on an oil facility in the kingdom, which has waged a three-year crackdown on Islamic militants - though al-Qaeda-linked militants have previously attacked oil company offices.
There was no immediate word on who was behind the attack, which took place in a region where Saudi Arabia's Shia minority is centred.
A Saudi journalist who arrived at the scene soon after the explosion said only one car exploded and that the guards killed two people in a second car before it blew up.
Guards then battled for two hours with two other militants outside the facility, the reporter said.
AP