Islamic militants in northwestern Pakistan have killed five teachers and two aid workers in what is thought to be retaliation for polio vaccination efforts in the region.

The teachers and aid workers were gunned down as they were returning from conducting vaccinations at a school for girls in the town of Swabi, according to the Associated Press.

The area where the attack occurred has been rife with violence, with several such instances occuring in the past few years. Khyber Pakhtunkhwa province has long been a hiding place for Islamic militants who utilize the region's proximity to Afghanistan to regularly carry out attacks in both countries.

There has not been a group to come forward and take responsibility for the attack. Local reports indicate the attack was in response to continued polio vaccination work that militants claim is making the Muslim population sterile and spreading pro-western propaganda.

In the same area in December, militants attacked aid workers conducting polio vaccination work, resulting in the deaths of nine workers nine workers' deaths.

And again in the same region in October, militants nearly killed 15-year-old Malala Yousufzai, who was advocating for girls education.

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Yousafzai was shot in the neck as she walked home from school. The 15-year-old had gained local notoriety for her criticism of the Taliban's ban on education for girls. She wrote a powerful blog that became known around the world and promoted education for girls just like her.

"I felt hurt on opening my wardrobe and seeing my uniform, school bag and geometry box. Boys' schools are opening tomorrow. But the Taliban have banned girls' education," Yousafzai wrote in 2009.

In the months since her ordeal, Yousufzai has gained worldwide recognition and inspired young girls across the globe. To aid in her recovery, she was transported to the United Kingdom, where doctors have regarded her recovery as a miracle.