Four people were killed including a soldier and two paramilitary troops when a bomb concealed in a plastic bag went off in Pakistan's northwestern tribal area near the Afghan border, officials said Saturday.
The incident occurred in the Khyber district when security officials spotted a suspicious plastic bag near a security checkpoint.
Khyber is one of the seven semi-autonomous tribal areas where the army has for more than a decade been battling militants linked to the Taliban and Al-Qaeda.
"As the security officials were inspecting the plastic bag, the bomb concealed in it went off, killing a solider, two paramilitary troops and a civilian," a local administration official told AFP, requesting anonymity.
The incident was confirmed by other local security officials.
There was no immediate claim of responsibility.
Violence across Pakistan has declined in recent years following a series of military offensives against insurgents but the remnants of militant groups are still able to carry out periodic bloody attacks, particularly in the northwest.
The army launched an operation in June 2014 in neighbouring North Waziristan to wipe out militant bases in the tribal areas and end an insurgency that has cost thousands of civilian lives since 2004.