Students at a Pakistani university where Taliban militants killed 21 people last week protested on Monday over a lack of security as authorities reopened the campus in the country's volatile northwest.

Four Pakistani Taliban gunmen stormed the Bacha Khan University in Charsadda on Wednesday, firing automatic rifles and throwing grenades as they raided classrooms.

At least 200 students gathered on the grounds of the university on Monday after the gates opened, shouting slogans against both the government and the Taliban.

"You must protect us!" they shouted, while also vowing to continue their education despite the threats.

There were to be no classes at the university on Monday.

"Some people aren't going to the university today as they have serious concerns about the incident and their personal security and that of the students," a teacher at the university said, on condition of anonymity.