Pakistani officials say a remote-controlled bomb exploded near a police van in the country's southwest Sunday, killing three passers-by and wounding at least one other person.

The officials say the blast took place in Quetta, the capital of the restive Baluchistan province bordering Afghanistan and Iran. They say the bomb was planted on a donkey cart.

No one claimed responsibility for the attack.

Baluchistan is home to various militant groups, including pro-Taliban factions, and Baluch separatists who are fighting a low-level insurgency in hopes of gaining political autonomy and a greater share of the profits from the region's natural resources.

Amnesty International says Baluchistan is one of the most militarized regions of Pakistan, where armed sectarian groups, government security forces and criminal gangs operate with impunity.