QUETTA: Separatist rebels on Tuesday shot dead four policemen and threatened to execute 21 hostages unless Pakistan withdraws paramilitary troops and releases detainees in the southwest, police said.

"The bullet-ridden bodies of four policemen were thrown by miscreants in the Naseerabad area and they were taken to the nearby town of Dera Murad Jamali," senior police official Shariq Jamal told AFP in Baluchistan province.

Insurgents last week took hostage a group of policemen and labourers. Last Thursday, four policemen were killed by the rebels, he said.

Another 10 policemen and 11 labourers remain in captivity in the province, which borders Afghanistan and Iran.

"We are trying to secure the release of hostages and have requested tribal elders to help us in this regard," Jamal said.

Rebel group spokesman Sarbaz Baloch, in a telephone call to reporters in Quetta, the capital of restive Baluchistan, claimed responsibility for the killings and gave authorities a Sunday deadline.

"We have killed four policemen today and the rest of the hostages will also be killed if, by Sunday, the government does not withdraw FC (Frontier Corps paramilitary) from Quetta and release our men," Baloch told AFP.

Pakistan deployed paramilitary troops in Quetta last month to help security after a spate of targeted killings blamed on Baluch rebels.

Hundreds of people have died since Baluch rebels rose up in 2004 demanding political autonomy and a greater share of profits from the region's wealth of natural resources.