Bahrain says it has taken legal action against some Shiite worshippers accused of mixing anti-government protests with annual religious ceremonies.

The crackdowns during the Shiite commemorations building toward Ashura — marking a seventh century battle in Islam’s early decades — could cause further tensions between Shiite religious leaders and the Gulf nation’s Sunni monarchy.

Opposition groups and others, including the U.S. State Department, have strongly denounced a government order last month to outlaw protest gatherings. The move seeks to quell a 21-month uprising by Bahrain’s majority Shiites seeking a greater political voice.

A government statement Sunday says “a number” of Shiite religious figures have been referred to the public prosecutor for delivering political sermons or leading anti-government chants.

Bahrain is home to the U.S. Navy’s 5th Fleet.