Police in northwest Pakistan say gunmen have attacked police officers who were guarding a team of polio vaccination workers, killing one of the officers and wounding another.
Officials say the police were attacked Saturday in Peshawar, the capital of the Khyber Pakhtunkhwa province.
No group has claimed responsibility for the attack.
Militants frequently attack polio workers in Pakistan, accusing them of being Western spies or part of a plot to sterilize Muslims.
The disease is highly infectious and can cause irreversible paralysis.
The Global Eradication Initiative says polio remains endemic in three countries - Afghanistan, Nigeria and Pakistan. The Initiative says until poliovirus transmission is interrupted in these countries, all countries remain at risk of importation of polio.