Nabeel Rajab is the president of the Bahrain Center for Human Rights. His lawyer, Mohammed al-Jishi, says the activist was “beaten brutally” by members of the security forces during a rally on Friday in the capital, Manama.
He says policemen hit Rajab on the head and face with sticks and kicked him.
The government says in a statement that police found Rajab “on the ground, injured while participating in an unauthorized march” in Manama.
Bahrain’s majority started campaigning for greater rights from the Sunni monarchy last February.
Dozens of people have been killed and thousands more have been arrested and put in jail or fired from their jobs in Bahrain since the beginning of the popular uprising in February 2011.
In addition, many health workers, teachers, opposition figures and human rights activists in Bahrain are still facing trial or serving prison terms over participation in anti-government demonstrations.
The Bahrain Independent Commission of Inquiry issued a report on November 23, 2011, saying that the Manama regime had used “excessive force, including the extraction of forced confessions against detainees” in their attempts to choke the demonstrations in the country.