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PESHAWAR, Pakistan - At least 12 security officials were killed and nine others injured in an attack Saturday as they escorted polio vaccinations teams in the Jamrud area of the Khyber tribal region.

Jehangir Azam, a government official in Jamrud, said armed men, believed to be militants, first targeted a convoy of security forces escorting polio teams through an improvised explosive ‎devices (IEDs) and then opened fire at them.

He said the men then attacked a second team of security forces that was trying to rescue the victims of the first explosion.

"Most of the injured died of their injuries as they couldn't be shifted to hospital on time due to firing by the militants," he said.

According to the government official, members of the polio teams suffered minor injuries but remained safe in both the attacks.

The injured security officials and polio workers have been transferred to a hospital in Peshawar.

Polio workers have been facing serious security problems from militants and religious extremists in Pakistan due to local propaganda against the vaccine.