At least 22 Pakistani soldiers have been killed in an explosion that hit an army convoy near the northwestern region of Bannu, intelligence sources said.
At least 30 others were injured in Sunday's blast, which took place next to a checkpoint in the area.
The bomb had been planted in a civilian vehicle, hired to transport paramilitary Frontier Corps troops.
Tehreek Taliban Pakistan (TTP) have taken responsibility for the attack, Al Jazeera's Kamal Hyder reported.
"A curfew has been imposed in the area after the attack in Bannu and both the military and security forces have cordoned off the area," he said.
"It appears the would be local collusion given the fact a civilian vehicle was hired."
The vehicle was hired by the paramilitary Frontier Corps, said police official Inyat Ali Khan from the Bannu region.
It was part of a convoy that was about to leave the military base in the town of Bannu and drive south to the North Waziristan tribal area, he said.
The convoy was part of a regular Sunday morning troop rotation going into North Waziristan, said a military source who did not want to be identified because he was not authorised to speak to the media.
The assault took place after the Pakistani Taliban vowed to increase attacks on security forces following the election of the group's new leader, Mullah Fazlullah, at the end of last year.
"With the help of God we claim responsibility for this. The army is our enemy. We will carry out many more attacks like this again," Pakistani Taliban spokesman, Shahidullah Shahid, said in a telephone call from an undisclosed location.