Fourty-two soldiers were martyred in a suicide attack at an army base in north-western distract of Malakand on Wednesday officials said the attack was likely revenge for a missile strike against an al Qaeda training camp.
"Forty-two recruits died in the attack and 20 others are hospitalised," a senior security official told AFP.
The government earlier said 35 recruits were killed and over 20 injured in the deadliest suicide attack against the army since it was deployed in the tribal regions bordering Afghanistan.
The attack occurred in north-western Dargai town in the tribal district of Malakand, which is a traditional stronghold of Tehrik-e-Nifaz-e-Shariat Mohammadi (TNSM) group.
TNSM was Banned by President Pervez Musharraf in January 2002, the group set up by firebrand cleric, Sufi Mohammad, sent 10,000 armed tribal fighters into Afghanistan to fight the US-led invasion of the neighbouring country in late 2001.
Mohammad was arrested in 2002, when he returned from Afghanistan and is still behind the bars.
"Malakand is a stronghold of TNSM and the attack appears to be a handiwork of the banned group," a senior security official told AFP.
The official, who requested anonymity, referred to recent statements by TNSM loyalists who threatened a wave of suicide bombings to avenge the army's raid on a madrassah run by the same group in neighbouring Bajaur tribal agency.
Pakistan military in its October 30 airstrike killed 80 militants. The government said the bombed seminary or madrassa was being used by two wanted TNSM clerics, Maulvi Faqir and Maulvi Liaqat, as a training camp for al Qaeda militants.
Liaqat was killed in the strike, while Faqir is still at large. The raid sparked angry protests in the tribal region with hardliners blaming US forces based in Afghanistan for the airstrike.
Chief military spokesman Major General Shaukat Sultan said the investigations were underway into Wednesday's attack.
"We strongly suspect the attack on the army center was done by the people trained in Bajaur in the madrassah run by al Qaeda facilitators Maulvi Liaqat and Maulvi Faqir," Sultan told AFP.
He said Faqir and Liaqat, who was killed in the madrassah raid, were linked to banned TNSM group.
Soon after the military's strike, TNSM supporters addressing thousands of armed tribesmen at public meetings in Bajaur openly threatened retaliation for the attack.
Hours after Wednesday's attack on the army camp, an anonymous caller claimed that the suicide attack was carried out by Pakistani Taliban.
In a telephone call to a senior Pakistani journalist Rahimullah Yousafzai said the suicide attack on the army training camp was in response to the military raid in Bajaur.
He said the bomber recorded a statement before the attack which would be released soon.
The caller claimed that a group led by Abu Kalim Mohammad Ansari had a list of 275 suicide volunteers. Security officials offered no comments on the claim.
TNSM, which has considerable following in the deeply religious tribal territories for advocating Islamic Shariat law, was targeted in a major army crackdown in late 1990s for attempts to impose a Taliban-style system in the region.