Taliban storms Pakistan university, leaving at least 21 dead

Gunmen stormed a university in northwestern Pakistan on Wednesday, leaving at least 21 people dead - four of them security guards - and dozens wounded.

Pakistani Taliban spokesperson Umar Mansoor claimed responsibility for the attack on Bacha Khan University, saying it was revenge for a previous operation by the Pakistani military.

Mansoor was behind the December 2014 attack on an army-run school that killed 144 children.

Police said the militants scaled the university walls and then entered the building, opening fire on students and teachers.

Police chief Saeed Wazir told AFP the operation had ended and security forces were clearing the area, with most of the student victims shot dead at a hostel for boys on the campus

Many of the dead were reportedly shot in the head, execution-style.

"More than 30 others including students, staff and security guards were wounded," Wazir said.

Meanwhile, military spokesman Major General Asim Bajwa said on Twitter that four attackers were killed.

"Update: Snipers killed 2 more terrorists on roof top, total Terrorist killed so far 4. All buildings (and) roof top taken over by Army," he wrote.

Pakistani Prime Minister Nawaz Sharif, who is currently in Davos for the World Economic Forum, issued a statement condemning the attack.

Sharif said he was "deeply grieved over the sad incident of terrorists' attack on Bacha Khan University”.