A roadside bomb exploded in northwest Pakistan on Wednesday killing an off-duty polio vaccinator and his relative while wounding another worker, officials said.
The blast occurred in the Ali Nagar village of the Mohammad tribal district along the Afghan border where Taliban militants are active.
The bomb went off near the house of polio vaccinator Mohammad Gul who was out walking with his brother, also a polio worker, and his cousin, although it was not clear whether they were specifically targeted.
"One polio worker (Gul's brother) and his cousin were killed while another polio worker was wounded," local government official Akbar Hussain told AFP.
Nobody claimed responsibility for the bombing, but militants have been aggressively targeting immunisation workers across Pakistan.
The militants allege polio vaccination is a cover for espionage or Western-conspiracy to sterilise Muslims.
Those conspiracy theories gained further traction after the CIA recruited a local doctor to start a vaccination programme during the hunt for Osama Bin Laden which dismayed many aid and health workers.
The number of polio cases recorded in Pakistan passed 200 for the the year last week, a 14-year-high.
Some 60 people including health workers and police providing security have been killed in militant attacks on polio vaccination teams since December 2012.
A local security official confirmed the bombing and casualties.
Officials said 136 cases reported were from the troubled northwestern tribal areas that border Afghanistan and are home to Taliban and Al-Qaeda militants.