Bahraini police have arrested prominent human rights blogger Zainab al-Khawaja, according to a rights group and a video posted online of her being roughed up, handcuffed and dragged away.
All the while, security forces continued to fire tear gas at sporadic protests in Shiite villages, the opposition said.
Khawaja had been taking part in a sit-in on a highway leading to the Gulf state's capital when police moved in to detain her on Thursday, the Bahrain Centre for Human Rights said.
Security forces fired tear gas and stun grenades to disperse the protest of hundreds of Bahrainis, while Khawaja, 27, and other women staged the sit-in on a roundabout, said the organisation.
A daughter of imprisoned leading activist Abdulhadi al-Khawaja, she was seen sitting on the grass before police moved in to take her away, the video footage posted on YouTube showed.
But while all other women fled the scene, Khawaja remained seated in the middle of the roundabout.
The footage showed her being handcuffed by a female policewoman.
Another female member of the security forces appears to grab Khawaja's face violently, before both dragged her to a police vehicle.
One of the policewomen can be seen punching Khawaja in the chest as she lay on her back on the pavement.
In its statement, the Bahrain Centre for Human Rights called for action to "guarantee her release and protection from further physical violence."
Another woman, Masooma al-Sayed, was arrested at another sit-in next to a mall on the same Manama highway, said the BCHR.
The interior ministry said two women were arrested after refusing to end their "illegal" assemblies.
It said the protester arrested near the mall, presumably Sayed, had "attacked one of the policewomen."
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The two were referred to the public prosecutor in the presence of their lawyer, said the statement.
A female officer "took my (Muslim head) scarf off and tied it around my mouth to stop me from speaking," Khawaja was quoted telling her lawyer Zahra Masood, in the rights group's statement.
The mother of a one-year-old child and whose husband Wafi al-Majed is in prison along with her father, Khawaja, is known on Twitter social network as "Angry Arabiya."
She tweeted from the roundabout before her arrest saying she was chanting "Down, down (King) Hamad" and that a "few girls" have joined her while "riot police don't seem to know what to do."
Said Yousif, a blogger and BCHR member, tweeted that the public prosecution had ordered to keep the two women in custody for seven days, and that a doctor check them following the claimed abuse.
US-based advocacy group Freedom House condemned the arrests, urging the government of the Sunni-ruled monarchy to honour its promise to introduce reforms.
"Despite its rhetoric to the contrary ... (the) crackdown calls into question whether the government of Bahrain is serious about real reform," said Daniel Calingaert, the group's vice president for policy and external relations.
"Bahrainis are sick of hearing that reform is on the way. They want to see tangible evidence, beginning with the ability to demonstrate peacefully without fear of prosecution," he added in a statement.
Bahrain's security forces used live ammunition and heavy handed tactics to crush mass Shiite-led democracy protests earlier this year.
A report by the Bahrain Independent Commission of Inquiry said last month it found police used "excessive force" and tortured detainees in a crackdown on the protests, and made a series of recommendations.
The report published on November 23 said the death toll from the unrest was 35, including five security personnel and five detainees who were tortured to death while in custody. Hundreds were also injured.
On Friday, police clashed with protesters in several Shiite villages outside Manama, Al-Wefaq main Shiite opposition said on its Facebook page, adding that several youths were arrested and beaten at the main roundabout in the village of Diraz.
Yousif tweeted that police fired tear gas at "peaceful" protesters in the village of Karranah, west of Manama, claiming that security forces have blocked several roundabout along Budaiya highway, and in the villages of Al-Qadam and Shakhurah, also west of the capital.