The Pakistani Taliban has claimed responsibility for an attack inside an army compound in northwest Pakistan that officials said left at least 22 soldiers dead.
The suicide blast targeted a vehicle in a convoy about to leave a military base in the town of Bannu and drive west to the North Waziristan tribal area, police official Inyat Ali Khan said on Sunday.
Military officials said that the blast, which hit one of the civilian vehicles hired to move troops, also left 38 more wounded.
"A vehicle-borne improvised explosive device caused the blast," a senior military official told AFP news agency, adding that the exact circumstances were unclear.
A spokesman for the Tehreek-e-Taliban Pakistan, Shahidullah Shahid, said in a statement that the attack had been carried out to avenge the death of Wali-ur Rehman, the group's former second-in-command. He was killed last year in a US drone strike.
"We will avenge the killing of every one of our fellows through such attacks," the spokesman said.
The explosion was heard and felt across the town of Bannu.
"I rushed out of my home and saw black, thick smoke billowing out of the cantonment's Razmak gate area," resident Sajjad Khan said. He said troops quickly cordoned off the area and ordered residents to go back inside their homes.
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.
In apparent retaliation for the bomb attack, army helicopters fired missiles killing three fighters, officials said.
The helicopters fired at a road in the village of Musaki situated in the same tribal region as the bombing earlier on Sunday, intelligence and civil administration officials said.
North Waziristan is considered a safe haven for al-Qaeda-linked fighters. Pakistani troop convoys are often hit by roadside bombs, but blasts inside military compounds are rare.
Last December, a suicide bomber killed four Pakistani soldiers when he rammed an explosive-laden car into a checkpoint outside an army camp in North Waziristan.
Thirty Pakistani troops died over a four-day period last April in another part of the northwest called the Tirah Valley as part of an operation to oust fighters hiding there.
The Pakistani military has been fighting for years in the tribal areas against fighters who want to overthrow the government.