Saudi Arabia is building up a special 35,000-strong rapid reaction force to protect its energy installations from attacks by militants targeting the world's largest oil exporter.

The kingdom started recruiting and training the industrial security force a year ago, after a failed al Qaeda attack on the world's largest oil processing plant at Abqaiq in February 2006.

The network's Saudi branch vowed more strikes on oil facilities after the attack, the first to directly target the kingdom's oil sector since militants began a campaign against the U.S.-allied Saudi royals in May 2003.

Al Qaeda's Saudi-born leader, Osama bin Laden, has called for it to take aim specifically at oil.

There is a new threat to oil installations from terrorists that has to be confronted, Interior Ministry spokesman General Mansour al-Turki told Reuters.

We can't just rely on a security system that was built some time ago for a different kind of risk.

Saudi Arabia pumps around 9 million barrels per day (bpd) of oil, over a tenth of global supplies, and severe damage to its infrastructure could have far-reaching effects.

The kingdom is keeper of most of the world's three million barrels per day (bpd) of spare oil capacity, a reserve crucial to the global energy system to deal with any surprise supply disruption.

The new force already has around 9,000 personnel either in training or already active, and will reach full strength of up to 35,000 in three to four years, Mansour said.

Companies from the United States and Britain were giving technical advice to the force, diplomatic sources said.

The new body will operate independently of other Saudi state security forces, allowing it to react more quickly to any threat, Turki said. The previous force of a few thousand was hamstrung by its reliance on cooperation from the police, the military or the Saudi national guard, he added.

What we are trying to do is ensure the force can take full responsibility for security so that these support forces are not needed, he said. Other forces have other responsibilities so can't always react as quickly.

The force will have its own budget, Mansour said, although he declined to detail how much.

INSIDE ARAMCO

The new force will be responsible for security outside the facilities of state oil giant Saudi Aramco. Aramco is also boosting security measures inside its compounds, but a company spokesman declined to give details.

Aramco has spent a total of $250 million in the past two years on building up security, a diplomatic source said.

Aramco is completely revamping its internal security, the source said. It always had very good commercial security measures, but that was not enough to deal with a concerted terrorist attack.

Even at the remotest facilities, Aramco is beefing up precautions. Deep in the Rub al-Khali desert, bright lights glare over the Shaybah oilfield facilities all night and the perimeter is guarded by a double fence.

At facilities like Shaybah, technology would be deployed including radar and night-vision cameras that sense and focus on any nearby movement, a diplomatic source said.

Aramco is working on boosting oil capacity at Shaybah by 250,000 bpd to 750,000 bpd by December 2008, part of plans to take output capacity to 12.5 million bpd in 2009 from 11.3 million bpd now.

So far, the kingdom has been successful in preventing attacks from threatening oil supplies, assistant oil minister Prince Abdulaziz bin Salman said.

Have you heard of any attacks lately? he said at a press conference this week. We believe we have taken every measure necessary to protect facilities and pre-empt any attempt. We take a great deal of pride in being a secure and reliable producer.

As the kingdom opened its doors this week to international media ahead of a summit for OPEC heads of state on November 17-18, filming of Aramco facilities was restricted.

A successful strike on the Saudi oil industry would be a major coup for al Qaeda, hitting at the heart of a decades-old alliance between the Saudi royals and Washington that Arab opposition groups across the region dream of seeing in ruins.

(Reporting by Simon Webb, additional reporting by Samira Kawar)