AL-QAEDA has threatened to launch further strikes to force “infidels” out of the Arabian peninsula after admitting responsibility for a suicide bomb attack on the world’s largest crude oil processing plant.

A local branch of Al-Qaeda said yesterday it had carried out the raid on the complex at Abqaiq, in the east of Saudi Arabia, which processes 5m-7m barrels of oil a day — up to 8% of the world’s consumption.

The bombing, named Operation Bin Laden Conquest, was part of efforts to prevent the “theft” of Muslims’ wealth by “crusaders and Jews”, according to a statement signed “Al-Qaeda in the Arab Peninsula” — the name of the terrorist network’s Saudi affiliate.

“There are more like them who are racing toward martyrdom and eager to fight the enemies of God, the Jews, the crusaders and their stooges, the renegade rulers” of Arab countries, the statement said. “You will see things that will make you happy, God willing.”

The huge facility, 35 miles from Dhahran, plays a pivotal role in the operations of Saudi Aramco. Besides the oil it processes itself, Abqaiq also handles an estimated 5m barrels a day from the Ghawar oil well. More than 90% of Saudi crude exports pass through the plant.

Al-Qaeda had long threatened to attack Saudi Arabia’s oil plants, but this was the first time it had tried to do so. Militants linked to the group had previously killed foreigners working in the oil industry, but had not targeted the facilities.

The strike sent oil futures in New York up $2.37 a barrel to $62.40 despite assurances by Ali Naimi, the Saudi oil minister, that production had continued without interruption. Analysts said prices would have risen by tens of dollars if the terrorists had succeeded in hitting the plant itself.

Naimi met Carlos Gutierrez, the American commerce secretary, in Riyadh, the Saudi capital, yesterday and assured him that the kingdom would “ensure the flow of oil despite the terrorist threats”.

Lieutenant-General Mansour al-Turki, a spokesman for the interior ministry, said the attack began at 3pm on Friday when two cars tried to drive through the gates of the outermost of three fences surrounding the processing facility. Guards shot at the cars and both vehicles exploded, causing a fire that was quickly controlled, he said.

This conflicted with unofficial reports that suggested the cars, both bearing Saudi Aramco logos, had succeeded in getting through the first gates but aroused the suspicion of guards at the second.

Two guards were critically injured in the ensuing gunfight and died later in the hospital, according to these reports. The bombers, wearing Saudi Aramco uniforms, then detonated the explosives in their vehicles. Several other people were also injured.

The attack, although thwarted, represented a serious blow for the Saudi authorities. The country suffered months of terrorist atrocities beginning in May 2003, when 35 people died in a series of bombings on compounds housing foreigners in Riyadh. But there had been no major incidents since December 2004, when terrorists stormed the American consulate, killing five employees.

Saudi authorities claimed afterwards to have crippled the insurgency by killing several Al-Qaeda leaders. They included Saleh al-Awfi, the organisation’s head in Saudi Arabia, who died in a gun battle with police in the holy city of Medina in August 2005.

Officials warned, however, that the group — which is believed to draw support from disaffected young Saudi men — will remain a threat in the kingdom for several years to come.

Bin Laden, who was born in Saudi Arabia, called for the overthrow of the Saudi royal family in 1990 during the build-up to the Gulf War after it allowed American military forces into the kingdom.

Security has been stepped up at oil facilities across Saudi Arabia, the world’s largest producer, in recent months in response to threats by Al-Qaeda.

In a statement issued before the attack Saudi Aramco said it remained “on alert at all times” to secure the world’s largest oil fields. The company is believed to employ 5,000 security guards who use helicopters, boats, cameras and other protection equipment.

Saudi Arabia holds more than 260 billion barrels of proven oil reserves, a quarter of the world’s total. It produces 9.5m barrels a day, equivalent to 11% of global consumption.

Some analysts tried to put a positive gloss on the attack, suggesting its failure showed the strength of security. For others, however, it appeared to have opened a new and potentially even more damaging front in Al-Qaeda’s campaign to undermine the West.

Michael Fitzpatrick, a New York-based oil expert, said Abqaiq was a “very tempting target for any opponent of the regime”, adding: “This forces us to focus on the worsening security situation in that part of the world.”

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