The State Department warned Wednesday that "imminent terrorist actions" could be aimed at U.S. interests in a region extending from Kuwait to Saudi Arabia, Bahrain, Qatar, the United Arab Emirates, Oman and Yemen.
"The United States government has strong indications that individuals may be planning imminent terrorist actions against U.S. interests in the Arabian Peninsula," the State Department said in a statement.
"In the past, such individuals have not distinguished between official and civilian targets. As always, we take this information seriously," the statement said.
A senior official said that Saudi Arabia and Kuwait were the focus of attention but that the other countries on the peninsula could not be ruled out.
The warning followed a communications intercept, said the official, who asked not to be identified.
The United States already has its embassies and other facilities in a state of heightened alert because of threats in the region, it noted.
"American citizens in the region are urged to remain vigilant with regard to their personal security and to exercise caution," the statement added.
The announcement supplemented a worldwide caution issued June 22 that warned Americans abroad of an increase in the risk of attacks.
That warning came a day after 14 people were indicted in the 1996 bombing that killed 19 U.S. servicemen at a military housing complex in eastern Saudi Arabia.