Officials say a northwestern Pakistani university where Islamic militants gunned down 21 students and teachers last week has reopened for classes amid tight security.

University official Kabir Khan says classes at the Bacha Khan University in the town of Charsadda resumed on Monday. Police official Iqbal Khan says extra security measures are in place.

The attack last Wednesday triggered a gunbattle that lasted for hours until all four militants who took part in the raid were killed. The assault shocked the nation and raised grim memories of the December 2014 massacre in the nearby city of Peshawar where the Taliban killed 150, mostly children.

Over the weekend, Pakistani officials said they arrested five suspects on charges of facilitating the Charsadda assault, which was claimed by a breakaway Taliban faction.