The US embassy in Saudi Arabia has warned Americans there to keep a low profile, following intelligence pointing to a potential terror attack.
Security forces claim to have killed several militants recently
An embassy statement referred to "indications of operational planning" by Islamist militants.
However, it said it had no information about the timing, target or method of a possible terrorist attack.
Since May 2003, militants in Saudi have frequently targeted Westerners in suicide bombings and kidnappings.
Militants loyal to Saudi-born al-Qaeda leader Osama Bin Laden have killed more than 90 foreign nationals and Saudi citizens and caused damage costing hundreds of millions of dollars.
Saudi Arabia has come under pressure to curb extremism in the wake of the violence and there have been regular gun battles between Saudi security forces and militants.
The kingdom says it is doing everything in its power to crack down on individuals and organisations linked to terrorism.