A government statement quoted Nayef Yousif, head of Bahrain's public prosecution, as saying al-Marzooq is accused of instigating violence and having links to a protest faction that authorities blame for bombings and other attacks. Al-Marzooq, who was detained Tuesday, was ordered held for 30 days during the investigation.
Al-Marzooq is a top member of Al Wefaq, the main political bloc of Bahrain's Shiite majority.
In Washington, State Department deputy spokeswoman Marie Harf said Wednesday that the U.S. would raise the issue with Bahraini authorities as part of its discussion of recent political events in Bahrain.
"We are disappointed that opposition groups have suspended their involvement. I think it's an important forum. We would hope that everybody would be part of that process," Harf said.
Also Wednesday, Bahrain's public security chief, Maj. Gen. Tariq Hassan al-Hassan, said a policeman died of injuries suffered in a bomb blast last month.