Two policemen were shot dead in a north-west district of Pakistan as they prepared to escort polio vaccination teams, triggering a temporary suspension of the programme in the area.
Gunmen shot dead the two officers as they were preparing to take up guard duties for vaccinators in Lower Dir district.
A spokesman for the Pakistan Taliban told Radio Mashaal that its militants were responsible. The killing followed the assassination of a female polio worker in Bannu district earlier this month.
Pakistan's door-to-door polio eradication programme has often come under attack from militant extremists who allege it is a Western plot to sterilise Muslims or to spy on locals.
The two dead men were named Farmanullah of Toormang and Mukkaram Khan of Sangolai, Dawn newspaper reported. Both were on their way to join a polio team in the Bishgram union council of Maidan.
Vaccinations were suspended in the neighbourhood and security was stepped up for other teams.
Pakistan and neighbouring Afghanistan are now the only two countries where the crippling virus remains.
n unprecedented 30-year campaign to stamp out polio virus is on the verge of ridding the world of a disease that struck around 350,000 victims a year as recently as the late 1980s. By contrast, there were only 33 worldwide cases in 2018. Donor countries and philanthropists pledged $2.6 billion in November to continue funding the "last mile" of eradication.
The final stretch has so far proven frustratingly difficult, however. The virus continues to find refuge in the two countries where conflict, local suspicion and unwelcoming terrain conspire to make vaccination difficult.
Cases in Pakistan have risen sharply, from 12 in 2018, to more than 100 so far this year. Militant violence and conspiracy theories that the drops are either harmful or a deliberate plot to sterilise Muslims, have badly undermined the vaccination campaign.
In neighbouring Afghanistan, the Taliban have refused permission for polio teams to work in many areas, leading to a growing pool of unvaccinated children.
An international monitoring board of experts set up to oversee the performance of the campaign last month warned that while eradication was still possible, the past year in Pakistan had been “an annus horribilis [horrible year] for the polio programme and a year of triumph for the poliovirus”.
The five-member board led by Sir Liam Donaldson, a former Chief Medical Officer of England, said teams in Afghanistan and Pakistan had “completely lost control of the polio eradication process”.
“It need not have happened,” their 64-page report went on. “It is a source of public embarrassment for the Global Polio Eradication Initiative and the two countries’ governments.”
The Pakistan eradication programme had overestimated its own levels of success in vaccinating people and underestimated the problems of deep-seated hostility and resentment towards the programme.
Moreover, the programme had become subject to political division, with disputes and factional fighting undermining performance.
Sewage samples show the virus is still circulating in many Pakistani cities, meaning the numbers of cases is likely to get worse before it gets better.
A major donor conference in Abu Dhabi in November saw countries and bodies pledge $2.6 billion (Dh 9.5 bn) to bolster the final push to wipe polio from the face of the Earth.