A bomb attack killed three people and wounded two others in a relatively peaceful area of Pakistan's northwestern tribal district early on Friday.
A father and his son were among those killed as they returned home from morning prayers in the Ambar area of Mohmand, one of the seven semi-autonomous tribal districts along the Afghan border.
"The improvised explosive device (IED) planted near the mosque exploded when people were returning home after offering morning prayer," Sikandar Shah, a local government official, said. All those killed and wounded were civilians, he added.
An official from the local tribal police confirmed the incident and casualties.
No group has yet claimed responsibility for the attack, but Mr Shah said that local tribesmen had launched an anti-Taliban militia and the incident might be a reaction to that.
Violence in Pakistan has declined in recent years following a series of military offensives against insurgents along the northwestern border. But the remnants of militant groups are still able to carry out periodic bloody attacks, particularly in the northwest.