The gunmen ambushed the vehicle near Khuzdar, around 200 km (120 miles) southeast of the Baluchi provincial capital, Quetta, they said.

"Five soldiers and a civilian were killed in the attack," military spokesman Major-General Shaukat Sultan told Reuters in Islamabad yesterday.

One soldier and a civilian were wounded, he said.

Sultan said the soldiers were in civilian clothes and were going on leave.

"It is an act of terrorism. We have launched investigations," he said.

The Baluch National Army (BNA), a shadowy militant group, claimed responsibility for the attack.

A spokesman for the BNA, who identified himself as Azad Khan, telephoned several newspapers offices in Quetta, claiming that the attack was in response to a military operation on Baluch militants.

He vowed more such attacks if the crackdown continued.

Pakistan security forces launched a massive operation last week in the Turbat area, around 380 km (225 miles) south of Khuzdar, following a similar attack in which two soldiers were killed.

Police blame Baluchi nationalists for the frequent attacks on security forces and government installations.

The nationalists demand more control over the area's natural gas and mineral resources as well as political and economic rights.

They are also vehemently opposing government plans to build three military cantonments in the province, saying that the government should allocate funds for development instead.

Trouble has been brewing in Baluchistan -- Pakistan's biggest, but the least populated and backward province -- for the past several months.

There have been a spate of rocket attacks and bombings in various Baluchi cities and towns, specially targeting the natural gas supply pipelines.

Thousands of paramilitary and regular troops have been deployed in the remote areas to protect the country's biggest natural gas fields and other government installations which are the main targets of militants.