The Pakistani Taliban claimed responsibility for a gun and explosives attack on a university in the country's northwest that left at least 21 people dead on Wednesday.

"Our four suicide attackers carried out the attack on Bacha Khan University today," Umar Mansoor, a commander in the Tehreek-e-Taliban Pakistani (TTP) militant group told AFP by phone from an undisclosed location.

Mansoor added that the attack it was in response to a military offensive against extremist strongholds in the tribal areas.