DUBAI, (Reuters) – An explosion rocked Saudi Arabia’s huge Abqaiq oil facility in the east of the kingdom on Friday and an official said Saudi forces had thwarted suicide bomb attacks against the world’s biggest oil exporter.

Oil jumped more than $2 a barrel. Al Qaeda leaders have previously called for attacks on oil fields in Saudi Arabia, a key U.S. ally.

A security source said suicide bombers had tried to storm the facility in the mainly Shi’ite province, known locally as Baqiq,and site of one of Saudi Arabia’s main oilfields.

“Security forces foiled an attempted suicide attack at the Abqaiq refinery using at least two cars,” the official said.

Dubai-based television station Al-Arabiya said Saudi forces killed the attackers. It quoted witnesses saying there was shooting.

Al Arabiya said the cars used by the attackers had the logo of Saudi state-owned oil company Aramco on them and that one car exploded at the gate to one refinery mid-afternoon.

Al Arabiya said a fire at a pipeline from the blast was now under control.

It was not clear if there was any impact on output from the world’s top oil producer and a close U.S. ally.

Most Saudi oil is exported from the Gulf via the huge Abqaiq producing, pumping and processing facility. The world’s biggest processing plant, it handles about two-thirds of the country’s output.

Former Middle East CIA field officer Robert Baer has described Abqaiq as “the most vulnerable point and most spectacular target in the Saudi oil system.”

“It’s not clear what damage there is but Abqaiq is the world’s most important oil facility,” said Gary Ross, CEO at PIRA Energy consultancy in New York.

“This just emphasises fears over global oil supply security when we’re already facing major ongoing risks in Nigeria, Iran and Iraq.”