U.S. military families will begin leaving Bahrain in the next few days following reports terrorists were planning attacks here, a spokesman for the U.S. Navy's 5th Fleet said Monday.

Cmdr. James Graybeal said the formal departure orders came late Sunday, two days after the Pentagon announced the first such mandatory evacuation from this longtime U.S. ally in the Gulf.

Graybeal said the orders affected 350 families, or about 650 people. They were relatives of service members or Defense Department staff, he said. He said earlier reports that nonessential staff also were being evacuated were incorrect.

"We are in the process of executing the departure, which will happen in the next few days," Graybeal said. Citing security, he refused to say how the families would travel or exactly where in the United States they were headed.

The U.S. 5th Fleet (search) is based in Bahrain, where the U.S. Navy has had a presence for more than 50 years.

On Thursday, the State Department cautioned Americans against traveling to Bahrain (search) and advised Americans who live there to leave because of information that extremists were planning attacks in Bahrain.

The Pentagon said Friday it was withdrawing service members' families from Bahrain for at least 30 days. The State Department added Saturday it had authorized the voluntary departure of family members and non-emergency employees of the U.S. Embassy in Bahrain.

The State Department (search) has provided no details on the information it has about possible terror attacks on Americans in Bahrain.

Bahrain is linked by a 15-mile causeway to Saudi Arabia, which has seen a series of attacks on Americans and other Westerners living there. Some here have expressed fears that Saudi militants, under pressure from their security forces, might see Bahrain as an easier place to attack Westerners.

The Saudi violence has been blamed on members of or sympathizers with Al Qaeda, the network of anti-Western Muslim extremists blamed for the Sept. 11 attacks on the United States. Al Qaeda has vowed to topple the Saudi royal family, accusing it of being too close to the United States and insufficiently Islamic.

The Bahraini king, Sheik Hamad bin Isa Al Khalifa (search), also is close to the United States. Sheik Hamad was one of the few Arab leaders to accept an invitation to last month's Group of Eight summit in the United States, where a U.S. initiative to encourage democratization in the Arab world was unveiled.

Saturday, Sheik Hamad said Bahrain was ready to send a naval force to help safeguard Iraqi territorial waters if asked by the new, U.S.-backed Iraqi government. Few other Arab leaders have been willing to commit troops for fear of being seen as supporting the U.S.-led war that toppled Iraq's Saddam Hussein.