Militants attacked an irrigation dam under construction in northwest Pakistan killing three workers and kidnapping at least two others, officials said on Wednesday.
Around a dozen gunmen attacked the Ghallanai dam site in Mohmand tribal district overnight.
Mohmand is one of the seven semi-autonomous tribal districts along the Afghan border -- an area that is rife with Taliban and Al-Qaeda-linked militants.
The attackers planted an improvised bomb on the road leading to the dam, which hit a vehicle carrying labourers, killing at least three people.
"At least two labourers and one contractor were killed and five others were wounded in the blast. The militants had earlier kidnapped two workers from the site," an administration official in Mohmand told AFP.
A security official confirmed the incident but put the number of those kidnapped at four.
No group immediately claimed responsibility for the attack.
Pakistan is a frontline state in the US-led "war on terror" and its government says more than 40,000 people have been killed in attacks in recent years.