Bahrain on Tuesday charged four US journalists with taking part in an illegal gathering but they were planning to leave the country after being released, their lawyer said.

The four, freelance journalist Anna Therese Day and three members of her camera crew, were detained on Sunday during protests marking the fifth anniversary of a Shiite-led uprising in the Gulf kingdom.

"They are at the airport waiting for a flight to leave the country," their lawyer Mohammed al-Jishi told AFP.

Manama's chief prosecutor Nawaf al-Awadhi said the four had been questioned in the presence of lawyers.

They were charged with "taking part in an illegal gathering with criminal intent and undermining public security," he said in a statement.

They were released pending further investigations, he added, and Jishi said the group were free to travel.

The four Americans were arrested in the Shiite-majority town of Sitra "as they took part with a group of saboteurs in acts of rioting and vandalism," Awadhi alleged.

One of them was masked at the time of the arrest, he said, adding that cameras and computers in their possession were seized.

The four entered Bahrain between February 11 and 12 and "provided false information" to authorities, claiming to be tourists, police said.

Day has reported extensively from the Middle East, North Africa and elsewhere, and her work has been featured in news outlets including the New York Times and CNN.

Her family said the four were committed journalists and denied they had done anything wrong.

The journalists' families confirmed their release.

"While we believe the four should not have been held at all, we are grateful to the Bahraini authorities for facilitating their timely release," the families said in a statement.

"We are awaiting news of their current location and hope they will be free to return to the United States as soon as possible."

Human rights groups criticised their detention, with the New York-based Committee to Protect Journalists branding Bahrain "one of the worst jailers of journalists in the Arab world".

Home to the US Fifth Fleet, Bahrain was rocked by an Arab Spring-inspired uprising demanding reforms and a constitutional monarchy on February 14, 2011.

Authorities crushed the protest movement one month later, but demonstrators have still taken to the streets and clash with police in Shiite towns surrounding Manama.