At least three security personnel who were guarding a polio vaccination team were killed on Tuesday in a bomb blast in Pakistan’s northwestern tribal region.

The officials were guarding a polio vaccination team in Salarzai area of Bajaur tribal region near Afghan border.

Three security personnel were killed and three persons, including two levies men and one civilian official, were injured in the attack, an official from the office of political chief of the district said.

A three-day-long polio campaign is going on in the agency and security was on high alert in the area.

At least 1,600 workers are taking part in the drive to provide medicine to 2,24,000 children in the district.

No one has taken responsibility yet but the country faces massive resistance to its anti-polio efforts by Taliban militants, who consider the vaccines a conspiracy to sterile Muslims and regularly attack polio workers and their police escorts to discourage immunisation campaigns.

Last month three levies personnel were wounded in similar attack in Bajaur during a polio campaign.

Militants have killed at least 64 health workers and their escorts as Pakistan suffered record 235 polio cases this year.

Pakistan, along with Afghanistan and Nigeria, are the only three countries in the world where polio remains endemic.

The WHO in May imposed travel restrictions on people travelling from Pakistan to other countries.