Pakistani officials said late on Friday Baluch separatists killed at least 21 passengers in the southwestern Baluchistan province after they forced off buses travelling from the western Pakistani city of Quetta to Karachi.
A group of terrorists -later estimated to be around 20- stopped two passenger buses and kidnapped 35 passengers, said the Home Minister of Baluchistan Sarfraz Bugti.
Bugti said bodies of 19 passengers, which were bullet-riddled, were found a few hundred metres away from where the incident took place, the number later raised to 21.
"The armed men were wearing the uniforms of the security forces," said Bugti.
He also said around 500 security troops participated in the operation against the gunmen, on which five of the passengers were recovered after an exchange of fire.
Baluch separatists have been fighting in Baluchistan, of which Quetta is the capital, for decades.
All passengers, who were killed in the attack, were Ismailis from Pakistan's minority Shia community.
The deadly attack reminded the tragic memories of another gun attack on a bus in which 45 members of tiny Ismaili-Shia community were killed earlier this month.