Manama: Bahrain expelled two American rights activists on Saturday after police used tear gas and stun grenades to break up a protest that tried to march towards the roundabout at the centre of a failed anti-government uprising last year.

The activists had come as part of a group called Witness Bahrain which says it wants to observe events on the eve of the February 14 anniversary of the uprising.

"Huwaida Arraf and Radhika Sainath arrived in Bahrain in the last few days and obtained tourist visas upon arrival at the airport," a statement from the government's Information Affairs Authority said.

"However, once in Bahrain, they declared their intentions to join demonstrations in order to report on them. Arraf and Sainath were picked up at an illegal demonstration in Manama this afternoon." It said they had already been deported but associates said they had not yet left the country.

A statement by Witness Bahrain said the women, human rights lawyers, were taking part in a peaceful demonstration.