Officials said Saturday that five Bahraini men, including at least one member of Bahrain's military forces, were arrested in the past one or two days for plotting terrorist attacks on the tiny island.
Police also seized guns and ammunition the group intended to use "for carrying out acts of terrorism targeting the security of the country and the people," the official Bahrain News Agency reported.
Bahrain's pro-U.S. king, Sheik Hamad bin Isa Al Khalifa, was quoted by the agency Sunday as saying he was alarmed "there are Bahrainis who have motives to cause harm to the safety of citizens and residents and to damage the economy of the country and its national security."
The king called the incident an "isolated case" but did not elaborate.
Officials did not reveal a specific attack plot and said investigations were under way.
One line of investigation was whether the group was planning to attack U.S. interests in Bahrain, including the U.S. Navy base housing the 5th Fleet, the officials said Sunday.
"We are looking at all possibilities and it is still early to say who or what their real targets were," said one official on condition of anonymity. "But we believe the prime targets could have been the Americans."
The U.S. Navy referred all questions on the matter to the U.S. Embassy, which declined to comment.
Bahrain authorities are investigating whether the group was part of a larger terrorist network, and whether more members were still at large. The arrests are the first terrorism-related detentions in Bahrain since the Sept. 11 attacks in the United States.
Pro-government newspapers on Sunday quoted unidentified religious sources as saying the five suspects — identified as Moheiddin Khan, Bassam Bukhowa, Bassam Ali, Isa al-Balouchi and Jamal al-Balouchi — were known for religious radicalism.
Isa al-Balouchi was a current member of the National Guard, part of the Bahrain Defense Forces, the Bahrain Tribune reported.
Security has been extremely tight at the Navy base since the United States began building up its military forces in the Gulf region in preparation for possible strikes on Iraq.
The United States accuses Iraqi leader Saddam Hussein of hiding weapons of mass destruction, and has threatened to disarm him by force. Iraq denies having banned weapons.
Bahrain hosts 4,000 American military personnel and may play a role in any U.S. military attack on Iraq.