QUETTA, Pakistan - Two policemen were shot dead on Tuesday while guarding a polio vaccination team in southwest Pakistan, officials said, the latest deaths in a high-stakes campaign to eradicate the debilitating virus. Pakistan and Afghanistan are the only countries in the world where polio remains endemic despite an effective vaccine, and anti-Islamabad militants have a history of targeting officers escorting inoculators. Two men riding a motorbike opened fire on the officers guarding a two-woman vaccination team working in the Nawa Killi area of Balochistan's provincial capital Quetta, police said. The policemen "died on the spot" while both women remained safe inside a house where they were inoculating children, senior police official Adeel Akbar told AFP. Local police official Masood Kasi confirmed the incident and said the officers were members of Pakistan's marginalised Shiite Hazara community. "We are investigating the incident from both the attack on the polio team and any potential sectarian elements involved," Kasi said. "We have further increased the security of the polio teams and the vaccination campaign is still ongoing," he added. No group has claimed responsibility for the attack, which comes just two days after an Islamic State suicide bomber killed 54 people at a political gathering in Pakistan's northwest. The Pakistan Taliban -- a separate group which shares common lineage with the Afghan Taliban -- have claimed previous assassinations of polio security escorts. Since the Taliban returned to power in Kabul in 2021, Pakistan has witnessed an uptick in militant attacks focused in regions along the border with Afghanistan. Pakistan has reported only one case of polio this year, but 20 were reported last year, according to the Global Polio Eradication Initiative. Efforts to end the disease have also been hampered by conspiracy theories spread by the radical religious right, which claim vaccination programmes are part of a Western plot to sterilise Muslims.