Former Shiite opposition MP Khalil Marzooq has been detained on charges of "promoting terrorist acts", authorities said on Wednesday, in a move slammed by the opposition as a "dangerous escalation".
Marzooq was questioned by prosecutors in the presence of his attorney and has been ordered held for 30 days for further investigation, Nayef Yousif, head of public prosecution, said in a statement.
Marzooq served as deputy speaker in the 40-member parliament before 18 MPs from the influential Shiite opposition bloc Al-Wefaq walked out in February 2011 protesting violence against demonstrators.
He was referred to public prosecution on Tuesday, the statement said.
"He was subsequently charged under the Law for Protecting the Community from Terrorist Acts, with inciting and advocating terrorism, and using his leadership position in a legally organised political society to incite crimes," it said.
Prosecutors also accuse Marzooq of being "affiliated with (a) terrorist organisation", the statement added, naming the radical February 14 Revolution Youth Coalition.
In June, authorities announced the arrest of several leaders of the cyber-group over suspected links to Iran.
Marzooq is also accused of "speaking at many forums, inciting and promoting terrorist acts, advocating principles which incite such acts, supporting violence committed by the terrorist coalition, and legally justifying criminal activities."
The English-language statement alleged that he incited "such acts" in his last speech on September 6.
Al-Wefaq described Marzooq's arrest "and keeping him as a hostage" a "serious and dangerous escalation taken by the regime in Bahrain."
It denounced "the aggressive, baseless, and fake accusations" against Marzooq.
Led by the influential Al-Wefaq, the opposition is taking part in a national dialogue that began on February 10 aimed at ending the country's political stalemate, while keeping up street protests to call for reform.
Bahrain, a strategic archipelago just across the Gulf from Iran, is the home base of the US Fifth Fleet and Washington is a longstanding ally of the ruling Al-Khalifa dynasty.
At least 80 people have been killed in Bahrain since Arab Spring-inspired pro-democracy protests erupted in February 2011, according to the International Federation for Human Rights.