The boats were spotted by a
Chinook helicopter on Monday
The soldiers and three civilians, including an oil contractor, were released but two civilian boat drivers remained in detention, said a spokesman for Central Command.
He had no information on the nationalities of the captains of the two boats or the detained drivers.
A US defence official, speaking to AFP on condition of anonymity, said they were detained in Iranian waters although the circumstances were unclear. Other officials said they were detained in the Shatt Al-Arab waterway.
Officials said the contractor was an employee of US company Kellog, Brown and Root while the soldiers were providing security.
Earlier on Monday the US Navy’s Bahrain-based maritime liason office said in a statement that two small civilian boats carrying the soldiers and civilians had disappeared in northern Gulf waters on Sunday.
The boats were on their way to Iraq’s only deep-water port Faw to pick up Iraqi oil company workers.
An investigation is underway into the incident to establish why the boats strayed into Iranian waters.