Sahibzada Anees, a local official, confirmed that violence had broken out again after a two-day lull, but he gave no casualty figures.
  
"We have sent troops to the area and are collecting details of the casualties," he told the AFP news agency.

Three people were also killed during an exchange of gunfire in Sadda town, officials said. Troops rushed to the area and brokered a truce between the warring groups.

Soldiers patrolling the streets of Parachinar, the main town in the Kurram region near the border with Afghanistan, have been given shoot-on-sight orders in an attempt to control the violence.

Tribal elders and clerics from the two sects have been trying to negotiate a ceasefire between the heavily armed rival groups.

Shias make up 20 per cent of Pakistan's 160 million population but are in the majority in Parachinar.

More than 4,000 people have been killed as a result of sectarian violence in the country since the late 1980s.