ISLAMABAD, Pakistan — The Pakistani Taliban has suffered its second major split in three months, with militant leaders this week confirming the emergence of a hard-line splinter group inspired by the success of the Islamic State in Iraq and Syria.

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.

The formation of Jamaat-e-Ahrar is one of the most serious internal threats to the Pakistani Taliban, officially known as Tehrik-e-Taliban Pakistan, since it was formed seven years ago.