Pakistani officials say a bomb hit an army vehicle escorting school children Wednesday, killing at least three soldiers and wounding 16 other people.

Authorities say nearly half of those wounded in the blast in the southwestern city of Quetta are in critical condition.

There was no immediate claim of responsibility for the attack.

Quetta is the capital of Pakistan's Baluchistan province. The area has been the scene of sectarian violence, militant attacks and unrest linked to a low-level insurgency.