Militants shot dead a kidnapped Pakistani army officer as his comrades were closing in to try to rescue him in the restive southwest province of Balochistan, the military said on Thursday.

Lieutenant-Colonel Laeeq Baig Mirza was abducted late on Tuesday as he travelled back to the city of Quetta from a hill station with his family and a friend, security officials said.

The separatist insurgent Balochistan Liberation Army (BLA) released a statement saying its fighters had seized Mirza, a rare attack on an officer of his rank in the region that borders Iran and Afghanistan.

Pakistan's military said its troops and helicopters started a search and rescue operation and spotted up to eight militants in a storm drain in nearby mountains late on Wednesday.

"On sensing their possible encirclement, militants shot the Colonel," the military's communications arm said in a statement. Two of the militants died in a gunfight but the rest escaped, it added.

Security officials said the militants had also abducted and killed the officer's friend, identified only as Umer, after stopping their car on the highway between Quetta and the hill station, Ziarat.

Umar's body was recovered in a different area in the mountainous region on Thursday, one official said, asking not to be named as they were not allowed to speak to the media.

The BLA and other separatist group have been waging an insurgency for years in Balochistan, a resource-rich region which has attracted substantial Chinese investment.

In April a suicide attack killed three Chinese teachers in Karachi, the capital of neighbouring Sindh province, drawing strong condemnation from Beijing. The BLA claimed responsibility.

In February, insurgents armed with bombs and guns attacked two Pakistani military bases in Balochistan, killing seven soldiers and losing 13 of their own men.