DUBAI/WASHINGTON (REUTERS) - A US 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.

Earlier, Bahraini police said they had detained four foreign nationals on Sunday. 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 US State Department said it was aware of reports that US citizens had been arrested but declined further comment, citing privacy considerations.

A spokesperson for Day's family rejected any suggestion that the four were involved in any illegal behaviour 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 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.

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