RIYADH, (Reuters) – Saudi Arabia has detained 520 suspected al Qaeda-linked militants since January, accusing some of them of planning attacks against an oil installation in the kingdom, the Interior Ministry said on Wednesday.

A ministry statement read out on Saudi television said the detainees were part of a wider plot managed from abroad and involving militant groups seized last year.

Among the detainees were some of Asian and African nationality. Some planned to use car bombs in attacks against an oil and a security target in coordination with al Qaeda second-in-command Ayman al-Zawahri who would send fighters from Iraq, Afghanistan and North Africa to back them up.

“Security forces managed to arrest one cell in the Eastern Province led by African residents … their concern was to get close to people working in the oil sector in order to find work in oil installations,” the statement said.

“They planned in fact to attack an oil installation and security target with rigged cars,” it added.

The kingdom, which has faced a campaign of violence by al Qaeda-linked militants since 2003, arrested hundreds of suspects in 2007 but because of a tough security crackdown has not faced any major attacks for over two years.

The ministry statement said a total of 701 people had been arrested in recent months but 181 had been released for lack of evidence, leaving 520 in custody.

The last major attack by militants was a failed attempt to storm at the world’s largest oil processing plant at Abqaiq in the Eastern Province in February 2006.

Saudi Arabia is the world’s biggest oil exporter and held a meeting of oil consumers and producers in Jeddah this week in an effort to tame record world oil prices.

The statement said the Eastern Province cell leader was found with a taped message from Zawahri.

The Interior Ministry warned Saudis last year to tell the authorities if they had received messages from the Egyptian Qaeda figure randomly on their phones or face consequences.

State television showed caches of ammunition and cash it said was found in possession of some of the suspects.

The detainees included another cell that was collecting funds in the Red Sea port city of Yanbu, the scene of an attack on foreigners working in the energy sector in 2004.

“They were acquiring money by any means including theft and fraud in order to fund terrorist activities inside and outside the country,” the statement said. “They tried to exploit religious sentiment in the country through Internet propaganda.”

Al Qaeda sympathisers — boosted by calls from Saudi-born Osama bin Laden to target the pro-Western Saudi government — have targeted foreign residential compounds, government buildings and energy sector installations since May 2003.

It was the biggest sweep of suspects since November when the authorities announced the arrest of 208 militants also planning attacks on oil installations. In December other suspects were arrested during the haj pilgrimage.