LONDON — Amnesty International urged Bahraini authorities Thursday to end a “heightened crackdown” on its opposition, after some 60 Shi’a clerics were summoned or arrested for participating in a protest.

The clerics were among scores of other demonstrators detained after taking part in a sit-in protesting the stripping of top Shi’a imam Isa Qassim’s citizenship.

“The Bahraini authorities should halt immediately their heightened crackdown on peaceful critics and opponents,” said the rights watchdog in a statement.

Bahrain has been shaken by unrest since security forces crushed protests demanding a constitutional monarchy and an elected prime minister in 2011.

Despite repeated calls from their Western allies, the kingdom’s rulers have made no concessions to the opposition and have intensified a crackdown on critics.

The Gulf manorchy is home to the U.S. Fifth Fleet.

Amnesty said four of the arrested clerics were sentenced to between one and two years in prison following the sit-in in the village of Diraz and nine others remain in detention and are facing trial.

It said most of the 60 have been charged with “illegal gathering” or “inciting hatred of the regime” as well as taking part in the Diraz protest.