Islamabad, June 28 : Two policemen and a polio worker were killed in an attack in Pakistan's Khyber Pakhtunkhwa province on Tuesday, as a nationwide drive to inoculate 12.6 million children against the virus is currently underway, sources said. The polio team escorted by police was administering vaccines to children in North Waziristan district, where all of the country's 11 new cases of this year were found, when they came under attack, the sources told Xinhua news agency. "Unknown gunmen opened fire at the polio team and fled the scene. A kid who was receiving drops also got injured in the attack," the sources said. The child was shifted to a nearby hospital. The sources added that the security had been put on high alert in the area after the attack, and a search operation was underway to arrest the perpetrators. No group has claimed the attack yet. The second Sub-National Immunisation Days (SNIDs) campaign is being held in all four provinces, covering 25 very high-risk districts across the country. Pakistan reported its latest polio case last week, detected in an eight-month-old infant in North Waziristan. All the 11 cases detected this year were reported in North Waziristan, with eight of them in the district's Mir Ali area. In a new report on June 24, the World Health Organization said Pakistan was among the four countries reporting the wild poliovirus besides Afghanistan, Mozambique and Malawi. /IANS