A Pakistani policeman was killed when militants attacked a polio vaccination team on Friday, police said, the latest casualty in the country's long campaign against the crippling disease.

Pakistan and neighboring Afghanistan are the only two countries where polio remains endemic and vaccination teams are frequently targeted by militants.

The latest incident occurred in Malik Din Khel, part of the former tribal border region that was once a haven for Taliban militants.

"Two gunmen riding a motorbike opened fire on policemen guarding a two-member polio vaccination team," district police chief Saleem Khan Kulachi told AFP.

"One policeman died at the scene while another sustained a minor injury," he said.

One of the gunmen was shot dead by police.

Local police official Zahir Ahmed Afridi also confirmed the details, adding that the healthcare workers were unhurt.

Pakistan initiated a week-long nationwide polio vaccination campaign on Monday, with the goal of inoculating more than 44 million children across much of the country.

There was no immediate claim of responsibility for the attack but Islamist militants, including the Pakistani Taliban, have killed scores of polio vaccination workers and their security escorts in the past.

Islamist opposition to inoculation grew after the US Central Intelligence Agency organised a fake vaccination drive to help track down Al-Qaeda's former leader Osama bin Laden in the Pakistani garrison town of Abbottabad.

Pakistan has reported five cases of polio this year, while 20 were reported last year, according to the Global Polio Eradication Initiative.