The U.S. Embassy in Saudi Arabia is warning that extremists may be planning to attack Westerners in the central province of al-Qassim.
A message posted on the embassy's website, and dated August 4, said officials there have received credible information about a possible attack.
It said the timing and method of the potential attacks are unknown and advises U.S. citizens to take necessary precautions.
The embassy says this is the first time this year it has warned of a possible attack by extremists.
Some information for this report was provided by AP, AFP and Reuters.