A bomb blast in Pakistan's southwestern province of Balochistan killed at least four people and wounded 15 others on Monday, officials said.

The bomb targeted a police vehicle in a busy market in Quetta, the capital of Balochistan, which is home to a separatist insurgency and several Islamist armed groups.

"Initial probe suggests that the explosion was caused by an IED (improvised explosive device) that had been planted on a motorcycle and was detonated using remote control," police official Azfar Mehsar told AFP.

"At least four people were killed in the incident -- that includes two policemen and two civilians," he added.

The Balochistan Liberation Army (BLA), a separatist group, claimed responsibility for the attack.

Wasim Baig, spokesman for the Sandeman Provincial Hospital in Quetta, confirmed the death toll, adding that the civilian casualties included a five-year-old girl.

The BLA made no mention of civilian deaths in their claim, saying only that two police officers were killed because of their involvement "in inhumane treatment of Baloch civilians under the pretext of investigations".

Pakistan has been battling a years-long insurgency by militants in Balochistan who are demanding a bigger share of the province's wealth, as well as attacks by Tehreek-e-Taliban Pakistan, also known as the Pakistani Taliban.

Tensions in the province have been stoked by a flood of Chinese investment under Beijing's Belt and Road Initiative that locals say has not benefited them.

China is investing in the area under a $54 billion project known as the China-Pakistan Economic Corridor, upgrading infrastructure, power and transport links between its far-western Xinjiang region and Pakistan's Gwadar port.