At least 21 people died when gunmen armed with grenades and Kalashnikovs attacked a university in Pakistan Wednesday, with all four attackers killed by security forces who moved in under thick fog to halt the bloodshed. The assault was claimed by a Pakistani Taliban faction but branded "un-Islamic" by the umbrella group's leadership, who vowed to hunt down those responsible. Police, soldiers and Special Forces swarmed the Bacha Khan university in the northwestern town of Charsadda from the ground and the air to try to shut down the assault. Television images showed female students running for their lives and witnesses reported at least two explosions. Pir Shahab, superintendent of investigations in Charsadda, said the 21 dead included one professor, two gardeners, one caretaker, and 17 students. Four attackers killed by security forces were not included in the toll, he said. Regional police chief Saeed Wazir, who also put the toll at 21, told AFP that most of the student victims were shot dead at a hostel for male students. An AFP reporter saw pools of blood and overturned furniture at the hostel, where security forces cornered the four gunmen. "More than 30 others including students, staff and security guards were wounded," Wazir added. He said the attackers had "taken advantage of the fog", adding that visibility was less than 10 metres (30 feet) at the time. Umar Mansoor, a commander of the Hakimullah Mehsud faction of the Tehreek-e-Taliban Pakistani (TTP), claimed responsibility for the attack. Security forces believe he was the mastermind behind a similar attack on an army-run school in nearby Peshawar in 2014 that left more than 150 people dead. The TTP's central leadership denied any involvement. "TTP strongly condemns today's attack and disassociates itself completely from this un-Islamic attack," spokesman Muhammad Khurasani said on Twitter, vowing that the group would bring those behind it to justice. The denial appeared to indicate continued infighting in the Pakistani Taliban, as the Islamic State group seeks to recruit its disaffected fighters.