Bahraini authorities have revoked the citizenships of 31 people, among them two former members of parliament, for having "undermined state security," state news agency BNA reported.
The names of the 31 activists, including brothers Jawad and Jalal Fairuz, both ex-MPs who represented the opposition Shia al-Wefaq party, were listed in Wednesday's report, which quoted an interior ministry statement.
Also named was Ali Mashaima, son of prominent activist Hassan Mashaima who is head of the Shia opposition movement Haq and who is serving a life sentence for allegedly plotting against the monarchy.
The government move comes after Bahrain late last month banned all protests and gatherings to ensure "security is maintained," after clashes between Shia-led demonstrators and security forces in the Sunni-ruled country.
The Gulf state, Bahrain, home to the US Fifth Fleet and strategically situated across the Gulf from Iran, has experienced unrest since February 14 last year when protests erupted calling for democracy.
Hundreds of people were arrested when the security forces, aided by troops from neighbouring Saudi Arabia, crushed the uprising within a month. However, protests resumed months later and happen on a regular basis in villages around the country.
Many activists, some whose names appear on Wednesday's list, were tried in a special military court set up at the time.
Another former MP and leading al-Wefaq member, Matar Matar, told AFP that some named on the list were acquitted by the military court while others were never charged with "undermining state security."
Other opposition sources said that some of the named activists are currently living abroad.
According to the International Federation for Human Rights, 80 people have died in Bahrain since the unrest began.
Two local rights groups -- The Bahrain Youth Society for Human Rights and the Bahrain Center for Human Rights -- voiced "grave concern" over the decision to revoke the citizenships.
"The BYSHR and the BCHR express grave concern over the systematic targeting of prominent political activists, former members of parliament, clerics and others," they said in a statement.
The decision, they said, "is intended to punish them for expressing peaceful dissent and thereby intimidate others from exercising their right to freedom of expression."
The groups called on the United Nations and world powers to persuade the authorities to "reverse this provocative decision" and to "immediately stop the systematic and widespread human rights violations against the citizens of Bahrain."
Tension has been running high in the kingdom following a spate of bombings on Monday in the capital Manama which killed two Asian expatriates. Four people have been arrested in connection with the bombings.
King Hamad ordered on Tuesday "the swift arrest of the terrorists who carried out the recent terrorist acts in Bahrain" and urged citizens to help "bring them to justice so they receive their punishment over this appalling act."
In a Wednesday statement, six Bahraini groups -- including al-Wefaq -- announced they reject and condemn "all forms of violence regardless of its source" and "defend the rights of citizens in free expression and peaceful gatherings."
The United Nations on Tuesday condemned the bombings. "These violent acts cannot be justified by any cause. We call on all concerned to exercise maximum restraint and to refrain from any provocations," said UN spokesman Martin Nesirky.