More than 1,000 members of the hardline Lashkar-i-Islami (Army of Islam) organisation gathered in Bara, a town bordering Afghanistan, to demonstrate against the rival Ansar-ul-Islam (Companions of Islam) group, they said.

Some armed members of the mob then marched towards a nearby village to attack the house of Ansar-ul-Islam's leader, Pir Saifur Rehman, a security official told AFP on condition of anonymity.

"In a bid to disperse the crowd, local tribal police and paramilitary units opened fire and six people were killed and 10 injured," the official said requesting anonymity.

Most of the victims were men in their late teens or early 20s, he said.

Lashkar spokesman Misri Khan said he knew of five people who had died on the spot and dozens of others who were wounded. "The number of dead could go up," he added.

The clash comes a day after police fired tear gas to disperse Lashkar-i-Islami activists who were protesting against the blowing up of the organisation's headquarters last week.

Officials said Lashkar's commander had set up a Taliban-style court in the building. The group was also behind the stoning and shooting to death of a woman and two men accused of adultery in March.

Last year, 25 people died in battles in Bara between supporters of the same two groups.