Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, sought to reassure Gulf states concerned that an increasingly militarized government in Iran might try to start a war.

"The United States takes very seriously our security commitments in the Gulf region," Mullen said following a meeting with Bahrain's king. Bahrain, directly across the Gulf from Iran, is home to a large US Navy base.

"We're very ready," Mullen said, an unusually direct acknowledgment that the United States has contingency plans to counter Iran should it make a move. "There are real threats to peace and stability here, and we've made no secrets of our concerns about Iran."

"Concerns about Iran's nuclear program are very real" among Gulf nations, said Adam Ereli, the US ambassador in Bahrain.

The US fears that if Iran masters the technical challenge of building a bomb it could set off a nuclear arms race around the Gulf.

"From my perspective I see Iran continuing on this path to develop nuclear weapons, and I believe that that development and achieving that goal would be very destabilizing to the region," Mullen said.

He gave no specifics about US plans or defenses, but the naval base is headquarters for ships and aircraft that monitor Iran and could be used to deter or defend against what military officials fear would be an attack that would come without warning. The base also houses Patriot missiles.

The US keeps tabs on Iran through extensive air surveillance in the Gulf and from naval patrols that regularly engage in formal communication with Iranian ships.