In response to the information, the embassy said it was restricting its American employees and their dependants from visiting housing compounds in the capital Riyadh at night.

"Recent confirmed information indicates that the Seder Village housing compound in Riyadh has been under active surveillance by terrorist elements," the embassy said in a warning to US citizens in the kingdom.

"Other Western compounds within the kingdom may also be targeted," the statement said.

The US warning comes three days after Britain reminded its 30,000 nationals in Saudi Arabia that militants might be in the final phases of planning attacks in the kingdom.

Last month, two Saudi suicide bombers killed at least 18 people, mainly Arab expatriates, at a Riyadh housing compound.

On May 12, the triple suicide bombing of three other housing complexes killed at least 35 people, including Americans and other foreigners.

Saudi authorities have blamed Saudi-born Osama bin Laden's al- Qaeda network for both attacks and the recent surge in militant-related violence in the kingdom.

Authorities said last week they had foiled an even bigger attack in Riyadh when security forces found a car primed with over 1.2 tonnes of explosives. Another 1.3 tonnes of explosive were found nearby.

Saudi Arabia, birthplace of Islam and most of the suicide hijackers who flew planes into US targets on September 11, 2001, has cracked down hard on militants since the May attacks.