ISLAMABAD - At least 12 people were killed and eight others injured on Tuesday morning when unknown gunmen opened fire at a vehicle in Pakistan's southwestern province of Balochistan, official sources said.

According to sources, the incident took place in the Akhtarabad area of the provincial metropolis Quetta when unknown armed men, riding a motorcycle, sprayed bullets on a passenger vehicle and killed five on spot.

15 other persons were injured who were transferred to the city's medical complex hospital where seven of them succumbed to injuries.

Sources said that the slain men belonged to the Shia Muslim community, who had been came under attacks by banned extremist groups in Balochistan province. The gunmen fled to unknown side after the attack before the police and other rescue team reached.

Security forces arrived at the scene and surrounded the area. Sources told that the vehicle at the Akhtarbabad area when it was taking 22 passengers from Quetta to the Dalbandin. The assailants stopped the vehicle and took out the people from the bus before spraying bullets at them.

No group claimed responsibility for the attack. The outlawed extremist group "Lashkar-e-Jhangi" claimed responsibility for several recent attacks on Shia Muslims. Dozens of Shia Muslims have been killed in targeted attacks in recent weeks.