Britain warned on Monday that militants were in the final stages of planning attacks in Saudi Arabia as Washington shut its missions there for two days and Australia told its citizens to avoid travel to the kingdom.
Saudi Arabia, battling a two-year campaign of violence by supporters of al Qaeda leader Osama bin Laden, said it had no solid information of any imminent attack in the oil giant.
"There are credible reports that terrorists are in the final stages of planning attacks," said an updated advisory posted on the Web site of the British embassy in the capital Riyadh.
Earlier, Britain cited "credible reports" that militants were planning attacks in the near future. It said Britons in the kingdom should maintain the highest level of vigilance.
AUSTRALIANS GET WARNING: Australia's Department of Foreign Affairs told Australians to avoid travel to the kingdom, saying militants might be planning attacks on housing compounds.
"We have received credible reports that terrorists are planning attacks in Saudi Arabia in the near future," the department said on its Web site.
"This follows other recent reporting suggesting that terrorists may be planning to attack residential housing compounds in Saudi Arabia."
The security warnings, combined with worries the United States may face a gasoline shortage, helped propel oil prices to another record high.
Saudi Arabia, the world's top oil exporter, already has high security around oil installations. Militants have waged a bombing campaign in the kingdom since 2003 to expel Westerners from Islam's birthplace and destabilise the pro-US government.
The warnings came a day after the American embassy in Riyadh said all US diplomatic missions would be closed on August 8 and 9 in response to threats of attacks on US buildings.
It warned of "ongoing security concerns" in the area, including for seaborne vessels travelling in the Red Sea.
King Abdullah, who came to power this month after King Fahd died, is expected to continue the crackdown on militants, which analysts say has eroded al Qaeda's network in Saudi Arabia.