The two Gulf nationals tried to enter Bahrain with forged passports through King Fahd Causeway.

Bahrain’s Interior Ministry said it has arrested two Gulf Arab citizens suspected of plotting “terror” attacks against the island kingdom.

The two Gulf nationals tried to enter Bahrain with forged passports through King Fahd Causeway, which joins Bahrain to Saudi Arabia, and were “carrying a large amount of money”, the ministry said late on Saturday.

“The initial investigation revealed that the arrestees are former detainees of the Guantanamo detention center. They are suspected of plotting a terror act to jeopardise the security and safety of Bahrain,” the ministry said in a statement.

The statement did not elaborate on the nature of the planned attacks or the identities of the two people arrested.

Bahrain, a Western ally which hosts the U.S. Fifth Fleet, has been hit by political unrest since protests led by majority Shi’ite Muslims erupted in 2011.

Authorities in Bahrain quelled the February 2011 revolt with help from Saudi Arabia and other Sunni-ruled Gulf states. But protests and clashes have persisted and talks between the government and the opposition have failed to end the crisis.