The convoy, heading to North Waziristan, was attacked by a remote-controlled bomb in the cantonment area near Aamandi Chowk, Razmak Gate on Bannu-Miranshah Road in Khyber- Pakhtunkhwa's Bannu.
The blast is suspected to have occurred in a rented car, part of private vehicles hired to transport the soldiers.
It was not immediately clear if it was a suicide attack. The Taliban have claimed the responsibility for the attack.
The convoy was attacked by a remote-controlled explosive
Security forces have cordoned off the area while rescue and relief operations continued. Sources said the death toll might increase.
Geo TV, quoting hospital sources, reported that 22 security men were killed while 38 have been injured.
The injured, including Frontier Corps and army personnel, were shifted to the Combined Military Hospital. Ten of the injured are in critical condition.
Bannu, which stands at the gateway to the semi-autonomous Waziristan tribal region, is 150 kilometres southwest of Peshawar.
The town has witnessed a number of attacks and was the scene of a massive jail break in April 2012, during which 384 prisoners escaped from its central prison.
President Mamnoon Hussain strongly condemned the blast that resulted into loss of precious lives.
Such cowardly attacks can never weaken the resolve of law-enforcing authorities and the nation to continue pursuing their struggle against the scourge of militancy and terrorism, the President said in his message.