Bahrain's public prosecution office said on Tuesday it had accused four US nationals of participating in an illegal gathering but ordered them freed pending further investigation.
The media campaign group Reporters Without Borders said on Monday that a US journalist and three members of her camera crew had been detained in Bahrain on Sunday, and urged their release.
It named the journalist as Anna Day, who has reported in the Middle East, north Africa, Asia and Latin America for numerous media outlets, mostly American.
The group's lawyer, Mohammed al-Jishi, told Reuters by telephone they were being transferred to a police station and should be released within an hour. He said the public prosecutor had not issued any decision that would prevent them traveling.
Public Prosecutor for Manama Nawwaf al-Awadi said in a statement that security forces had arrested the four Americans while they were "participating with a group of saboteurs who were carrying out riot acts in Sitra."
Sitra is a Shi'ite village east of Manama where clashes between demonstrators and security forces have been taking place this week to mark the fifth anniversary of Arab Spring protests in 2011, mainly by Shi'ite Muslims demanding reforms and a bigger share in government.
The prosecution statement, carried by the Bahrain News Agency, said the four Americans had been interrogated in the presence of their lawyers.
It said the group had been found with cameras and computers, and were accused of "disturbing public order and exposing modes of transport to danger."
A witness told Reuters that the three men and a woman had left the prosecution office in a white minivan with tinted windows, followed by a police patrol car.
The US State Department had said it was aware of reports that US citizens had been arrested but declined further comment. The US Embassy in Bahrain could not immediately be reached for comment.