At least 19 people have been killed after a bomb struck a pair of buses carrying Shia Muslim pilgrims in southwest Pakistan, a local official has said.

Zubair Ahmed said the attack on Sunday in Balochistan province's Mastung district wounded at least 15 people, including three women.

The bomb was strapped to a motorcycle and detonated by remote control. One bus was almost completely destroyed. The other was damaged. 

Ahmed said the buses were coming from neighbouring Iran, a majority Shia country and popular destination for religious pilgrims.

There was no claim of responsibility for the incident.

Al Jazeera's correspondent Kamal Hyder, reporting from Islamabad, said there were suggestions that a suicide bomber had carried out the attack but "according to the deputy commissioner the device was a remote control bomb that targeted the bus and not a suicide attack as reported earlier".

"At the time at least three buses were travelling in close proximity of each other," our correspondent said.

Pakistan has experienced a spike in killings over the last year by radical Sunni Muslims targeting Shias who they consider heretics. 

Many attacks have occurred in Balochistan, believed to be a hiding place for senior Afghan Taliban commanders and also the site of a decades-long insurgency by nationalists.

Source: Al Jazeera and agencies