Hours after the shooting a man hurled a grenade at a shop near a mosque injuring four people. — AP

PESHAWAR Gunmen killed two Shia Muslim brothers on Sunday in a drive-by shooting in a northwestern Pakistani town troubled by sectarian violence, police said.

The attackers, who were riding on a motorbike, opened fire on the two men in the main bazaar of Dera Ismail Khan town before fleeing the scene, local police officer Naimatullah Khan said.

'The victims who died on the spot were brothers. They belonged to the Shia community,' he told AFP.

Hours after the shooting a man hurled a grenade at a shop near a Sunni Muslim mosque injuring four people, said Ashiq Saleem, a senior official at the local hospital.

Police officers confirmed the attack.

The incident triggered tensions and shops and markets were closed in the area of Dera Ismail Khan near the mosque, residents said.

Dera Ismail Khan district, which borders Pakistans restive tribal region, is a flashpoint for violence between the minority Shia and majority Sunni communities.

Shias account for some 20 per cent of Pakistans mostly Sunni Muslim population of 160 million.

Although the two groups usually coexist peacefully, more than 4,000 people have died in outbreaks of sectarian violence since the late 1980s.