ISLAMABAD, Pakistan - A police officer guarding polio vaccination workers in northwestern Pakistan has been shot dead.

It is the latest attack on polio vaccination teams, and those guarding them in the country.

The latest attack took place Tuesday in the northwestern province of Khyber Pakhtunkhwa, in the Karak district.

Karak District Police Officer (DPO) Irfanullah, according to Dawn, said a search operation was underway to catch the culprits.

KP Inspector General of Police Sanaullah Abbasi said that the officer's killers will be caught soon.

The team of polio health workers the slain officer was providing security for were unharmed.

Officials said their vaccination work would continue despite the attack.

According to the National Emergency Operations Centre (NEOC) for Polio, teams comprising 285,000 frontline polio workers are currently undertaking a one-week programme across Pakistan to vaccinate 40 million children under the age of five.

Polio workers and their security details have been coming under attack since a doctor involved in vaccinating for polio, in collaboration with U.S. intelligence agencies, identified and confirmed the location of former al-Qaeda leader Osama bin Laden, who was subsequently assassinated in a night-time lighting raid by U.S. Navy Seals.

To further justify their attacks, militant groups claim the vaccinations are part of a plot by Western countries to sterilize Muslims.

One of the worst attacks was in March 2014, also in northwest Pakistan, when eleven police officers protecting polio-vaccination teams were killed, and scores injured, in a roadside bombing and subsequent gunfight.

That attack took place in the Khyber tribal region near the city of Peshawar.

Pakistan is one of the last countries to still have cases of polio. A worldwide initiative, PolioPlus, by Rotary International to end the disease has been largely successful. The organization, now backed in its efforts by the WHO, and the Bill and Melinda Gates Foundation, has almost succeeded in eradicating polio. Africa, one of the last bastions, was declared wild polio-free last year. Only Pakistan and neighboring Afghanistan are still reporting cases.

(File photo. Credit: EPA).