Questions rise about whether security forces are able to protect country's educational institutions

Pakistanis buried their dead and observed a day of nationwide mourning on Thursday following the brazen attack by Islamic militants who stormed a northwestern university the previous day, gunning down students and teachers and spreading terror before the four gunmen were slain by the military.

The death toll from the assault at Bacha Khan university in the town of Charsadda has risen to 21, after another student died in hospital, said police official Tariq Khan.

Most of the victims were students and their families were inconsolable.

Two teachers were among the dead, including a chemistry professor who was praised as a hero for shooting back at the attackers and allowing some students to escape.

"My son was grown up, but still he was an innocent kid for me," said Gula Bibi, the mother of the second slain teacher, Iftikhar Ahmad, who was also the university librarian.

"My heart is breaking apart, I don't know what to do," she said.

The attack, which also wounded 22 students, raised grim echoes of the 2014 school massacre in the nearby city of Peshawar that left 150 dead, 144 of them children. It yet again raised questions about whether security forces are able to protect the country's educational institutions from extremists.

Flags on official buildings and the Parliament were flying at half-staff and police stepped up security at schools and educational centers across the country.

Peshawar assault

A breakaway Taliban faction claimed responsibility for the assault - the same faction, headed by Khalifa Umar Mansoor, which had claimed the Peshawar school assault.

The university in Charsadda is named after one of Pakistan's greatest secular leaders, Abdul Ghaffar Khan, also known as Bacha Khan. The attack coincided with the 28th anniversary of Bacha Khan's death on Jan 20, 1988.

Most of the victims were buried quickly, according to Muslim tradition, with funerals overnight and early Thursday, said Khan, the police official.

A spokesman Mohammad Khurasani for the main larger Taliban group in Pakistan disowned the group behind the university attack, terming it "un-Islamic" and insisted the Pakistani Taliban were not behind it.

Wednesday's violence yet again exposed the vulnerability of schools in Pakistan, where extremists have sought to prevent Western-style education, especially for girls.

The Bacha Khan university remained closed and its Vice Chancellor Fazal-ur-Rahim Marwat said classes would resume on Monday.

AP - AFP