"The American embassy in Riyadh advises all American citizens living in Saudi Arabia that it has received indications of operational planning for a terrorist attack or attacks in the kingdom," the US embassy in Riyadh said in a statement on Wednesday.
"The embassy has no specific information concerning timing, target or method of any possible attack(s)."
Hours after the embassy published its warning, Saudi Arabia's Interior Ministry said security forces uncovered a hideout 60km southeast of Riyadh where insurgents had stored more than two tonnes of bomb-making equipment.
The cache included fertiliser, ammonium nitrate, aluminium powder, potassium nitrate and other chemicals used by suspected al-Qaida fighters to make bombs deployed in attacks on Western housing compounds and security forces buildings.
Security forces which searched the hideout on Tuesday also found pipe bombs, acid and electrical equipment.
"The embassy has no specific information concerning timing, target or method of any possible attack(s)"
US Embassy statement
Saudi Arabia has been battling a two-year wave of violence by supporters of Saudi-born al-Qaida leader Osama bin Laden trying to expel Westerners from the country and destabilise the pro-Western royal family.
The US embassy statement, which briefly pushed oil prices up 60 cents a barrel, advised Americans in Saudi Arabia to keep a low profile.
"It isn't a result of any specific new threat, except that there are ongoing, credible threats," said Angela Aggelar, spokeswoman for the Consular Affairs division of the State Department in Washington.
"It's just one of our frequent warnings to Americans in the area, to remind them that the security situation there is always pretty grave."
Bombers hit several compounds in 2003 where foreigners were housed and armed men waged a series of attacks against Westerners last year, including a daylight raid on the US consulate in the Red Sea city of Jedda.
Saudi security forces have also been targets, the last high profile strike being a bombing in December outside the Interior Ministry in Riyadh.
The authorities have killed or arrested all but three men on a list of 26 most wanted suspects published in 2003. Last month they issued a list of 36 more wanted men they are still hunting.
Saudi police are hunting for
One of those suspects, Muhammad Ibrahim al-Hayyari, was killed in a fierce gun battle in Riyadh two weeks ago.
Insurgents have killed 91 foreign nationals and Saudi civilians in the last two years, Saudi officials say.
Forty one security force members and 112 insurgents have also been killed in clashes.