Bahrain Mirror (Reuters): A U.S. journalist and three members of her camera crew were detained in Bahrain on Sunday, Reporters Without Borders said on Monday, urging Bahrain to release the four American citizens "rapidly and without harm."

In a statement, the group described Anna Day and her three colleagues as experienced journalists, who had most recently worked on virtual reality documentaries in Egypt and Gaza.

Bahraini police said earlier they had detained four foreign nationals. Bahrain's interior ministry said in a statement the four were "suspected of offences including entering Bahrain illegally having submitted false information to border staff, and participating in an unlawful gathering."

The U.S. State Department said it was aware of reports that U.S. citizens had been arrested but declined further comment.

A representative for Day's family rejected any suggestion that the four were involved in any illegal behavior or non-journalistic activities.

The Arabic-language Mira'at al-Bahrain (Bahrain Mirror) said the four were detained in Sitra, a Shi'ite village east of Manama, on Sunday while covering clashes between local demonstrators and security forces.

The demonstration was meant to mark the fifth anniversary of widespread Arab Spring protests in 2011 mainly by Shi'ite Muslims demanding reforms and a bigger share in government.

Those protests were put down violently by Bahrain security units with help from security forces from Gulf Arab states, including Saudi Arabia. But the kingdom, where the U.S. Fifth Fleet is based, continues to see bouts of unrest, especially in villages where Shi'ites are a majority.

A friend of Day's, who asked not to be named because of her own work as an independent journalist in hostile areas, said that government accreditation for foreign correspondents in Bahrain can be difficult to get and can imply restrictions, so freelancers commonly work without it.

"It is sad that the fifth anniversary of the 2011 protests has been marked by the arrest of yet more journalists in Bahrain, which has since become one of the worst jailers of journalists in the Arab world," said Sherif Mansour, the Middle East and north Africa program coordinator for the Committee to Protect Journalists, an international advocacy group.

The Committee called for the release of the four and noted that at least six other journalists are currently imprisoned in Bahrain in connection with their work.

Day has reported in the Middle East, northern Africa, India, Brazil and Mexico and her work has been published by the New York Times, CNN, Al Jazeera English, Huffington Post, CBS, Daily Beast and other media.