UNKNOWN gunmen have killed a polio vaccinator in Pakistan's restive southwestern province of Baluchistan, highlighting resistance to the country's immunisation campaign, officials say.

The shooting happened in the Killi Jeo area of provincial capital Quetta a day after a three-day campaign kicked off across the country, senior government official Tariq Mengal told AFP.

Baluchistan, which borders Afghanistan and Iran, is plagued by sectarian violence between the minority Shi'ite and majority Sunni community, as well as by Taliban attacks and a separatist insurgency.

The Taliban have banned immunisations in some areas, condemning the campaign as a cover for espionage since a Pakistani doctor was jailed after helping the CIA track down al-Qaeda chief Osama bin Laden using a hepatitis vaccination program.

In Tuesday's incident, a team of male and female vaccinators was engaged in a door-to-door campaign to administer polio drops to children below five years of age when unknown gunmen on a motorbike shot dead a male volunteer, Mengal said.

"We are investigating if the dead man had any dispute with the attackers or the shooting was carried out by opponents of the campaign," he said.

The campaign has been suspended in several areas of Quetta as the shooting sparked fear among the vaccinators, he said.

"We will assess the security situation before resuming the campaign on Wednesday," he added.

Killi Jeo is home to thousands of Afghan refugees and local tribesmen.

Pakistan is one of only three countries where the highly infectious crippling disease remains endemic, along with Afghanistan and Nigeria.

There have been 30 confirmed cases of polio in Pakistan this year according to the government, 22 of them in the tribal areas bordering Afghanistan.