The convoy was headed from Bannu to Miranshah when it was targeted by the suicide bomber on the Mir Ali Bypass.

The injured were shifted to Mir Ali Headquarter Hospital.

Additional troops arrived at the site of the incident with a search operation underway, sources added.

The incident is the latest in a series of attacks on law enforcement by heavily-armed militants, particularly but not limited to areas bordering Afghanistan in the north-western Khyber Pakhtunkhwa district.

On Monday, two soldiers were martyred when militants opened fire on a checkpost in the Adam Warsak area of South Waziristan. Two days earlier, two soldiers were martyred in another attack - also in North Waziristan.

In one brazen incident, militants held a police officer hostage for almost 12 hours in a mountainous area of Swat.