US Assistant Secretary of State Richard Boucher stopped in Quetta, the capital of gas-rich Baluchistan province, on Thursday afternoon for talks on improving security along the border with Afghanistan.

The outlawed Baluchistan Liberation Army claimed responsibility for the ambush on Thursday night. The group wants more autonomy for ethnic Baluch people and a bigger share of the region's natural resources.

The attackers pumped bullets into the back of an open van carrying soldiers returning from home leave in other parts of the country, leaving bodies piled up in a blood-stained heap, an AFP photographer said.

Eight soldiers and one policeman were killed instantly and four people were wounded. One of the injured died in hospital overnight, said doctor Ghulam Haider of the Quetta Civil Hospital.

The attack happened directly outside the city's railway station. Police said up to four attackers followed the victims in a Suzuki car and fled after the attack.

Senior police officer Rahul Khan Brohi told AFP that 17 people had been arrested in raids overnight.

"They are being interrogated," Brohi said. More arrests were expected as raids continued Friday, he added.

Security has been tightened in Quetta where police set up roadblocks and stepped up patrols.

The attack was the deadliest on security forces in Baluchistan since the army killed rebel tribal chieftain Nawab Akbar Bugti in his cave hideout in August 2006.

"We launched the attack to avenge the killings of our innocent people in military operations including bombing raids," Baluchistan Liberation Army spokesman Beeberg Baluch said in a telephone call to Quetta press club.

"It was a retaliatory strike and such attacks will continue," he vowed.

President Pervez Musharraf said last month that his forces had eliminated almost all of the more than 60 Baluch rebel camps. He also offered an amnesty offer to tribesmen and announced 2.2 billion dollars in investment.

But the rebels oppose all involvement of the federal government in the province's affairs, claiming that it is creaming off profits from gas and mineral reserves in Baluchistan.

Hundreds of people including civilians have been killed since the tribal rebellion -- which has no known links to the Islamist Taliban insurgency along the Afghan-Pakistan border -- flared up in late 2004.

The rebels have attacked Pakistani security forces, railway tracks, power plants and other government facilities. Pakistan's military has replied with major military offensives.