An army convoy was hit by a mine planted near the town of Miran Shah in the troubled North Waziristan region bordering on Afghanistan, TV reports said.
No groups have so far claimed responsibility for the explosion. Analysts say radical Islamist groups are likely to be behind the attack, which occurred hours before President Pervez Musharraf is to be sworn for a new five-year presidential term.
On Wednesday, Musharraf stepped down as military commander amid opposition demands and international pressure.
The president has ruled the country since seizing power via a military coup in 1999, sharing the posts of civilian leader and military commander. In 2004, he pledged to relinquish military command, but had until now failed to fulfill the promise, citing instability in the country and a persisting threat from Islamist radical elements.
The tribal area in the northwest of the country harbors hundreds of Islamists, including Al-Qaeda and Taliban members. In early November, three Pakistani border-guards were kidnapped and killed in the area.