"There is a threat, I can't tell you the level of specificity or anything else," said a senior State Department official on condition of anonymity.
Officials in Saudi Arabia earlier said oil installations in the country were a "high-probability potential target" for terrorist attack, but tight security measures were in place.
State Department spokesman Sean McCormack meanwhile noted in Washington that there had been calls by al Qaeda to attack Saudi oil facilities in the recent past.
A Bahrain-based spokesman for Iraq coalition forces, Lieutenant Commander Charlie Brown, said precautions were being taken to deal with the threats.
"Coalition forces are taking prudent, precautionary measures and focusing maritime security operations in the Gulf on these possible threats," he said.
Saudi Arabia pumps more than nine million barrels of oil per day and sits on a quarter of global oil reserves. World crude prices quickly firmed on Friday on news of a potential terrorist threat to oil installations in the OPEC kingpin.

Copyright AFP (Agence France-Presse), 2006