The new group, known as Jamaat-e-Ahrar, is composed of disaffected Taliban factions from four of the seven tribal districts along Pakistan’s border with Afghanistan, according to a video released by the group. Counterterrorism experts said the group was effectively controlled by Omar Khalid Khorasani, an ambitious Taliban commander with strong ties to Al Qaeda.

Mr. Khorasani’s faction, which is based in the Mohmand tribal agency near Peshawar, had emerged as one of the most active Taliban elements this year. It is believed to have carried out a bombing in Islamabad that sought to derail peace talks between the Taliban and Prime Minister Nawaz Sharif’s government…

In a lengthy video statement explaining the decision to break away, Mr. Khorasani said the Taliban had become undisciplined and suffered from factional infighting. “This was devastating for our movement,” he said…

“Now the T.T.P. is ours, not theirs,” Mr. Ehsan said in a phone interview. Mr. Fazlullah’s Taliban faction has come under heavy assault by the Pakistani military in the North Waziristan tribal district. The army said that since the start of the offensive in June, it had killed over 500 militants, although the figures could not be independently confirmed. On Aug. 15, a senior Pakistani general said that the operation was in its “final stages” and that most of the area had been cleared of militants.