PARACHINAR: An explosion in Upper Kurram tribal region killed two anti-polio workers on Thursday, DawnNews reported.

Government administrator Yousuf Rahim says the men were going to a village to vaccinate children when the bomb hit their motorcycle in Upper Kurram tribal region on Thursday.

Although it's unclear whether the workers were the actual target, it was the second attack this week against polio workers.

On Tuesday, gunmen riding on a motorcycle killed a policeman protecting a polio vaccination team.

Pakistan is one of three countries where the crippling disease is endemic.

Suspicion for the attacks falls on militants, who oppose the vaccination campaign, accuse health workers of acting as spies for the US and claim the polio vaccine is intended to make Muslim children sterile.