Suspected militants attack Pakistan polio protection team
Two policemen who were escorting a polio vaccination team have been shot dead in Pakistan's north-west Khyber Pakhtunkhwa province.
The policemen were attacked by unidentified gunmen in the Dera Ismail Khan district.
More than 40 people linked to the polio vaccination programme have been killed in Pakistan since 2012.
The Taliban oppose the polio programme and have been responsible for similar attacks in the past.
They say the vaccinations are a cover for foreign espionage.
Militants have also accused health workers of being part of a Western plot to sterilise Muslims.
A bomb attack on a polio vaccination team in north-west Pakistan killed at least 11 people earlier this month.
In Tuesday's violence, a roadside bomb went off as the police-guarded convoy drove through a village near the Afghan border.
The blasts were reportedly followed by a fierce gun battle between security forces and the militants.
Pakistan is one of only three countries where polio remains endemic, along with Nigeria and Afghanistan.
According to the World Health Organisation, Pakistan recorded 91 cases of polio last year, up from 58 in 2012.