Earlier Wednesday, police an explosion hit a convoy carrying reinforcements to Mohmand and killed three soldiers and a civilian.
Local police official Akhtar Ali Shah said initial reports suggested that a suicide bomber carried out the attack near the town of Charsadda. Several other people were injured.
U.S. officials are urging Pakistan to keep up the pressure on Taliban and al-Qaida militants in their strongholds along the frontier, despite growing tension with archrival India over the terror attacks in Mumbai.
Adm. Mike Mullen, the chairman of the U.S. joint chiefs of staff, discussed Pakistan's offer to help probe the Mumbai bloodshed with President Asif Ali Zardari and military chiefs in Islamabad on Wednesday.
Mullen urged Pakistan to "investigate aggressively any and all possible ties to groups based in Pakistan," the U.S. Embassy said in a statement.
While noting recent Pakistani military successes against extremists in the border regions, Mullen "encouraged Pakistani leaders to take more - and more concerted - action against militant extremists elsewhere in the country," the statement said.
