Authorities in restive southwestern Pakistan say security forces are searching for a polio vaccination team that disappeared Friday evening.
The team included two vaccinators, two security personnel and a driver. The incident occurred near Zhob district in Baluchistan province.
Local health workers and relatives fear the team was kidnapped by militants.
Meanwhile, in the northwestern part of Pakistan, officials say gunmen ambushed another polio vaccination team Saturday, killing the driver.
Authorities said the attack took place in a restive tribal region near the Afghan border. A second team member was unharmed when the attackers fired at their van.
There has been no immediate claim of responsibility for the attacks.
The two incidents took place as Pakistan prepares for a three-day vaccination drive against polio that begins Monday.
Authorities say that attacks on polio vaccinators in Pakistan within the past four years have left nearly 70 people dead, including security personnel escorting the teams during national immunization drives.
The violence has undermined anti-polio efforts in Pakistan, where more than 85 percent of the world's cases were located last year, according to the World Health Organization.