At least eight people were killed on Tuesday, as warring Sunni and Shiite Muslims defied a self-declared ceasefire in Pakistan's Khurram tribal district, officials said.

The fresh wave of sectarian violence has swept through Khurram since early August, with running clashes leaving about 500 people dead and more than 700 injured.

"Heavy gunfire from both sides killed eight tribesmen and wounded more than 15," an official in the semi-autonomous tribal region said, seeking anonymity.

According to the official, the casualty toll could increase as the fighting was still raging, with scores of pro-Taliban militants crossing into Khurram from adjoining lawless regions to join the Sunni Muslims belonging to the Bangash tribe.

The Bangash, along with five other tribes in Lower Khurram, announced a ceasefire on Monday after almost 100 people were killed in the conflict's most violent clashes last weekend.

The rival Shiite Toori tribe also called a truce earlier in veneration of the Muslim fasting month of Ramadan that commenced this week.

Sectarian violence gripped Khurram in April 2007 and the region has been inaccessible through roads as armed men from the warning factions have blocked the routes. Several convoys carrying food and medical supplies were also attacked and destroyed.

Thousands of local people have relocated to safer places but are persistently asking the government to bring peace to Khurram.

A large crowd staged a protest demonstration against the Khurram clashes and road blockades in the capital Islamabad on Monday, suspending traffic on the city's main artery for hours.