A car bomb attack on buses carrying Shiite Muslim pilgrims to Iran killed 19 people and injured 25 in Mastung on Sunday, officials said.

The remotely-triggered bomb hit a convoy of three buses in Mastung district and set one of them ablaze, said Tufail Baluch, a senior government official in the district.

"At least 19 people have been killed and 25 injured. All of them were Shiite pilgrims," he told AFP, adding most of those killed were burnt to death.

"The bomb was planted in a car. The condition of some of the injured is critical," Baluch said.

Some 180 Shiite pilgrims were on their way to Iran in the buses when the bomb ripped through one of them, said Akbar Hussain Durrani, a senior government official in Quetta, the capital of Baluchistan province.

One bus carrying some 45 pilgrims was badly damaged, he said.

Mastung is some 30 kilometres (18 miles) south of Quetta.

There was no immediate claim of responsibility for the attack.

President Asif Ali Zardari has condemned the killing of pilgrims in a bomb explosion in Mastung.

In a condolence message‚ the President expressed sympathy with the bereaved families and directed the concerned officials to extend best medical facilities to the injured people.