Four Americans were being held by security forces after they were stopped for "suspicious" activity in the centre of Baghdad on Thursday, the governor of Baghdad province told AFP.
The two men and two women were driving a BMW with local license plates, rather than diplomatic registration, and were all wearing flak jackets and armed with pistols and automatic weapons, said Salah Abdul Razzaq, who described the group as "gunmen."
"They (security forces) stopped them, they checked their (personal ID) badges, they found them suspicious," he said, adding that the group had been stopped at 9am (0600 GMT) in the Sharchiyah neighbourhood of central Baghdad.
The four were still being held as of 3pm (1200 GMT), Abdul Razzaq said, but had not been charged with any offence. It was unclear how much longer they would be held, and whether they would be charged.
Abdul Razzaq did not provide any details about the four, whom he said had been visited by a US embassy official.
The US embassy did not immediately respond to requests for comment from AFP.