Bahrain's government confirmed the arrest of Khalil al-Marzooq, a deputy leader from the opposition al-Wefaq organization. He was accused of inciting violence and supporting terrorism through a speech he delivered last week.
The government stripped dozens of political activists of their citizenship, including at least one member of al-Wefaq. Bahrain blames the opposition group for unrest in the Persian Gulf country.
Dozens of people were killed during an uprising in 2011. Bahrain said it is committed to reforms outlined by an independent commission probing the government's response to the protests.
U.S. State Department spokeswoman Marie Harf said recent developments in Bahrain suggest it's not serious about reform.
She said in a statement Thursday Washington "notes with concern" restrictions placed on political and civil rights in the country.
"We also note with concern the detention of opposition leader Khalil al-Marzooq," she said.
The British Foreign and Commonwealth Office has warned of the potential for violence in Bahrain every Friday for at least the past three weeks.
The official Bahrain News Agency had no reports of violence or demonstrations Friday.