ISLAMABAD - At least six people were killed and 19 others injured in a suicide attack targeting the headquarters of paramilitary forces in Pakistan's southwestern Balochistan province on Tuesday, rescue and security officials said.

The attack took place in Quetta, the provincial capital, when terrorists rammed an explosive-laden vehicle into the main gate of the Frontier Corps headquarters, security sources told Xinhua on condition of anonymity.

They added that accomplices of the attackers managed to enter the vicinity after the blast, and an exchange of fire is underway.

Muhammad Zeeshan, operations manager of Edhi Foundation, a non-governmental organization, in Quetta, told Xinhua that a bus and a rickshaw were passing by the site when the explosion occurred, and most of the injured were passengers aboard the vehicles.

The injured were shifted to the Civil Hospital Quetta, where several remain in critical condition, he added.

No group has claimed responsibility for the attack yet.