Sept 2 (Reuters) - Saudi Arabia has strengthened its energy security since 2006, prompted by an al Qaeda attack on an oil plant and due to tensions with regional rival Iran.
On Tuesday, a small fire broke out on a gas pipeline in the kingdom's Eastern Province after unidentified assailants shot at a security patrol, Saudi security and oil industry sources said.
The pipeline has been repaired and there was no impact on oil or gas production, the sources said, but the incident marks the first confirmed attack on physical energy infrastructure in the world's largest oil exporter since 2006.
An August 2008 U.S. assessment revealed in a Riyadh embassy cable released by WikiLeaks, said facilities remained "highly vulnerable" and any disruption was likely to have a "devastating impact on the U.S. national economy and the global economy as a whole".
A cyber attack on national oil company Saudi Aramco's computer systems in August 2012 underscored the shifting nature of the threat.
Below are some main facts about Saudi energy security.
Saudi concerns about energy security sharpened considerably in 2006 when al Qaeda attacked the Abqaiq oil plant, which then handled about 70 percent of Saudi crude with a capacity of 7 million barrels a day.
The attack failed, but the U.S. ambassador said in a March 2006 cable the attack had been "much closer to succeeding than generally acknowledged".
Fears of an attack on Abqaiq were accentuated by a lack of spare parts for a plant built in the 1970s, meaning damage might be very hard to repair, said an August 2008 cable.
Soon after Abqaiq, the Saudi and U.S. governments started working together on ways to improve security at the kingdom's energy facilities.
An August 2008 cable said the U.S. Department of Energy had given Saudi Arabia access to a rigorous threat model developed by Lockheed Martin subsidiary Sandia Laboratories to protect nuclear facilities.
In September that year, a formal joint commission on critical infrastructure protection was set up by then Secretary of State Condoleezza Rice and Saudi Interior Minister Prince Nayef.
An American vulnerability assessment of the Abqaiq plant concluded its facilities were "world class" and would now be enough to counter a repeat of the failed 2006 attack.
In March 2007, then Saudi security chief Prince Mohammed bin Nayef estimated the threat to Saudi oil facilities as coming 60 percent from al Qaeda and 40 percent from Iran. In a conversation recorded in an embassy cable he asked how damage could be minimised "when at war with Iran".
His deputy Major General Saad al-Jabri said in a cable from April 2007 the Saudis feared a "layered" assault comprising military strikes, militant attacks and a popular uprising among minority Shi'ite Muslims in the Eastern Province.
Jabri said even an inaccurate "stupid" missile could cause serious damage to Saudi oil operations.
Saudi officials said in October 2008 that 25 critical oil production-related sites in the kingdom were vulnerable to militant attack at that time, according to a contemporary embassy cable.
Alongside oil industry facilities, there were risks to energy production from possible strikes against electricity or water plants, such as the Jubail desalination unit, which "provides Riyadh with over 90 percent of its drinking water".
The cable said the current structure of the Saudi government could not exist without the Jubail desalination plant and that if it was seriously damaged, the capital would have to be evacuated within a week.
NEW SAUDI FORCE
The "Facilities Security Force", or FSF, was set up in 2007 by the Interior Ministry to protect critical infrastructure, such as oil complexes and electricity and water plants.
The force was to have 35,000 members, Jabri said in an October 2008 cable. He added its numbers would be boosted by an extra 20 percent to aid port and border security.
He said it would provide a force of 5,000 maritime personnel protecting coastal and off-shore oil facilities like the Ras Tanura export hub.
(Reporting By Angus McDowall, Rania El Gamal; editing by William Maclean and Keiron Henderson)