Bahrain Mirror (Reuters): Bahraini police have detained four U.S. citizens, including one who was masked and taking part in a riot, a senior police official said on Monday, and local media reported they were journalists covering a protest.

The other three were detained at a checkpoint in the same area outside Manama, the director of police in the capital said in a statement that described the alleged rioters as vandals.

The police chief said the four had entered the country as tourists on Feb. 11 and 12 but some of them "carried out media activity without a licence from the concerned authorities, in addition to committing acts that violate the law".

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

It published photos of a masked person it said was a journalist for the Huffington Post website who was running with his hands in the air while being chased by two policemen. It said the photos had been published by activists on social media.

The demonstration was meant to mark the fifth anniversary of massive 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 island kingdom, where the U.S. Fifth Fleet is based, continues to suffer from bouts of unrest, especially in villages where Shi'ites are a majority.

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