The statement said: "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.

"They planned in fact to attack an oil installation and security target with rigged cars [car bombs]."

Other cells were said to have been broken up which planned attacks on economic targets in the world's largest oil exporter.

Foreign co-ordination

Some of the plots were said to have been hatched in co-ordination with Ayman al-Zawahiri, the al-Qaeda second-in-command.

The statement said that those organising people to come from abroad had taken "advantage of the facilities granted to the Muslim faithful to come to Mecca for the annual pilgrimage or to do the omra," or minor pilgrimage".

One cell member was said to have been found with a taped message from al-Zawahiri.

The kingdom has suffered several attacks blamed on al-Qaeda and mainly targeting westerners since 2003, but a crackdown has quelled attacks over the past two years.