Gunmen riding a motorcycle killed two members of Pakistan's Shia Muslim minority on Monday in an apparent sectarian attack, police said.

The killing took place in the suburbs of Quetta, the provincial capital of the south-western province of Baluchistan, while the victims were travelling in a rickshaw.

"Gunmen on a motorcycle stopped the rickshaw and then opened fire on them and fled the scene," Abdullah Jan Afridi, a senior police officer in Quetta, told AFP.

Afridi said the pair, from the Hazara ethnic group, were labourers in a coalmine. The rickshaw driver was unhurt in the attack in the Saryab road area.

"We are investigating but apparently it is a sectarian attack," Afridi said.

Noor Baloch, a police surgeon in Quetta civil hospital, told AFP both victims were shot in the head.

There was no claim of responsibility.

Baluchistan, which borders Iran and Afghanistan, has oil and gas resources but is afflicted by Islamist militancy, sectarian violence between Sunni and Shia Muslims and a separatist insurgency.

Sectarian violence -- in particular by Sunni hardliners against the Shia that make up roughly 20 percent of Pakistan's 200 million people -- has claimed thousands of lives in the country over the past decade.