The head of a breakaway Taliban faction behind an attack at a north-western Pakistani university that killed 21 people has threatened to carry out more attacks on schools and universities.

Khalifa Umar Mansoor said in a video released on social media on Friday that the attack at the Bacha Khan university in the town of Charsadda was just the start. He said his group will hit the "evil democratic" system at its base.

Mansoor, the Charsadda attack mastermind, said Pakistan's educational institutions provide the future workforce for the military and the government - all of which work against the "will of God".

The video also shows the four attackers who are said to have carried out the university assault practising with assault rifles at an undisclosed location.