Abqaiq, Saudi Arabia ? Suicide bombers carried out a bold attack on the world’s largest oil processing facility Friday but were stopped from breaking in by guards who fired on their cars, exploding both vehicles and killing the attackers.

Al-Qaida purportedly claimed responsibility for the attack, the first on an oil facility in Saudi Arabia. The assault raised speculation that the militants were adopting the tactics of insurgents across the border in Iraq, where the oil industry has been repeatedly targeted.

Saudi Oil Minister Ali Naimi quickly announced that the attack “did not affect operations” and that Abqaiq operations and exports “continued to operate normally.” The huge Abqaiq processing facility near the Persian Gulf prepares about two-thirds of the country’s oil output for export, making it a crucial link in getting Saudi crude to the market.

Crude oil futures spiked more than $2 a barrel amid fears militants would again target the vital industry. Light sweet crude for April delivery surged as high as $63.25 a barrel before settling at $62.91, an increase of $2.37 on the New York Mercantile Exchange. Brent crude futures for April delivery jumped $2.06 to $62.60 on London’s ICE Futures exchange.

The attack in Abqaiq, about 25 miles inland from Saudi Arabia’s eastern Gulf coast, took place about 3 p.m. – several hours after the weekly prayers on Friday, a day off for Saudis though the facility was in operation.

At least two militants were killed in the explosions, and Saudi-owned Al-Arabiya television reported two security guards also died. Interior Ministry spokesman Lt. Gen. Mansour Al-Turki could not confirm the deaths of the security guards but said two were critically wounded with potentially lethal injuries.

The assault began when two cars tried to drive through the gates of the outermost of three fences surrounding the processing facility, al-Turki told The Associated Press. Al-Arabiya reported that the attackers’ cars bore the logo of Aramco, the state oil company that owns the facility.

Guards shot at the cars, and both vehicles exploded, al-Turki said. The explosions caused a fire that was quickly controlled, the oil minister said.

Guards then battled for two hours with two other militants outside the facility, said a Saudi journalist who arrived at the scene soon after the explosion. He said he saw workers repairing a pipeline.