Peshawar, December 27:

Clashes between Sunni and Shiite Muslims this week in remote northwestern Pakistan have left at least 21 dead and 120 wounded, a doctor said today.

Authorities imposed a round-the-clock curfew in the Kurram tribal area after the violence broke out four days ago, Dr Nasir Ali said at a state hospital in the main town of Parachinar. He said doctors were performing surgery until 3 am today.

Many of the victims had gunshot wounds, and the curfew was likely preventing others from reaching hospitals, Ali said.

Kurram, a semi-autonomous region near Afghanistan, is prone to sectarian violence. In April, fighting sparked by an attack on a Shiite mosque left about 50 people dead. Then in November, three days of clashes left 91 dead before the warring sides declared a cease-fire.

It was not immediately clear why the cease-fire broke down this week.