A roadside bomb attack Monday in Kurram killed three soldiers and wounded two others, officials said.
A captain was killed along with two other soldiers when their vehicle hit an improvised bomb in Masuzai area of Kurram tribal district, a security official told AFP.
Another security official in Peshawar, confirmed the attack saying the troops had been patrolling around 30 kilometres (18 miles) east of Parachinar, a major town in Kurram district.
Pakistani troops have been locked in deadly battles for years with homegrown insurgents in the northwestern tribal belt, where Taliban and al Qaeda-linked militants also plot attacks on Afghan and Western targets.
Kurram also suffers from sectarian violence between majority Sunni Muslims and minority Shias.
A recent surge in sectarian violence has raised questions over security as Pakistan prepares for a general election expected in May.
Islamabad says more than 35,000 people have been killed as a result of terrorism in the country since the 9/11 attacks on the United States.