QUETTA: Thousands of people protested in Quetta on Wednesday after four police officers were shot dead in what an official said was a sectarian attack against Shias.

The four officers were killed when gunmen riding a motorbike sprayed their vehicle with bullets on a main road on the outskirts of Quetta, the capital of restive gas-rich Balochistan province, which borders Afghanistan and Iran.

The province, which has been in the grips of an insurgency for more than four years, has also been the scene of sectarian attacks between Sunnis and Shias.

More than 4,000 people carried the bodies of three of the officers, all Shias, through the streets to the home of a top military official, to demand justice, an AFP photographer at the scene witnessed.

Protesters called for a military probe into the killings before dispersing peacefully.

'Shiites have been targeted in the province for quite some time and the latest attack was directed against Shiite officers,' said provincial minister Jan Ali Changezi, who participated in the protest.

The killing was later claimed by Lashkar-e-Jhangvi (LJ), a banned Sunni Muslim extremist group with links to Al-Qaeda.

'We claim the responsibility for today's attack,' Ali Haider, identifying himself as a spokesman for the group, said in telephone calls to local media.

Earlier, senior police official Humayun Jogezai told AFP the officers had been shot dead in their vehicle as they were travelling to a training academy.

A high-ranking police official also sustained serious injuries.

Shias account for about 20 per cent of Pakistan's 160 million-strong, Sunni-majority population.

The groups usually coexist peacefully but outbreaks of sectarian violence have claimed more than 4,000 lives across Pakistan since the late 1980s.

Earlier, senior police official Humayun Jogezai told AFP the officers had been shot dead in their vehicle as they were travelling to a training academy.

Jogezai said no one had claimed responsibility for the attack, in which one high-ranking police official also sustained serious injuries.

Hundreds of people have died in violence in Balochistan since an insurgency flared in late 2004, with militants demanding political autonomy and a greater share of profits from the region's natural resources.

The province has also been hit by attacks blamed on Taliban militants.