Bahrain has slapped terrorism charges on an activist who tweeted criticism of the government's treatment of women, Amnesty International said Wednesday.

Ebtisam al-Saegh was accused of "using human rights work as a cover" to communicate with the Geneva-based Al Karama foundation, and of undermining Bahrain's "status abroad", Amnesty reported.

She was detained after retweeting a series of posts on July 3 critical of the king and National Security Agency.

Representatives of Bahrain's justice ministry were not immediately reachable for comment.

A statement carried on the state-run BNA news agency said four people were facing "terrorism charges", without naming them.

A group of UN special rapporteurs on Tuesday warned Saegh may be subjected to "acts of torture" in detention.

The activist had previously been arrested and released in May and has accused Bahraini security services of torture and assault during her detention.

"Saegh is a prisoner of conscience who must be immediately and unconditionally released," said Amnesty's Samah Hadid.

"By charging her with terrorism for her work on human rights, the Bahraini government is itself attempting to intimidate and silence civil society in Bahrain."

Sunni-ruled Bahrain has been gripped by unrest since 2011, when a wave of protests erupted in the Shiite-majority kingdom to demand an elected government.

Authorities have since cracked down on all dissent, jailing hundreds of protestors and stripping clerics and high-profile activists of citizenship.

The government has accused neighbouring Tehran of provoking unrest in the tiny kingdom, which lies across the Gulf from Shiite Iran.

Bahrain, an ally of the United States and home to its Fifth Fleet, has come under frequent criticism from international human rights groups for its crackdown on protestors.

Source: AFP