At least 21 killed in attack on Bacha Khan University in Charsadda, Pakistan

Islamabad, Pakistan (CNN)

Militants raided a university in northwest Pakistan, timing their attack to a ceremony at the school to ensure maximum casualties.

As security forces combed the campus block by block after the massacre Wednesday, they counted the bodies of at least 21 students. Four militants were also killed, said army spokesman Lt. Gen. Asim Bajwa.

The attack took place at Bacha Khan University in Charsadda, Peshawar — less than 40 kilometers (25 miles) from where the Pakistani Taliban slayed 145 people, including 132 children, in another college attack in December 2014.

It’s unclear whether the group was responsible for the Wednesday incident.

One Pakistani Taliban spokesman, Umar Mansoor, said the attack was in retaliation for military operations against the group. Mansoor was also the mastermind behind the December 2014 attack, Pakistan’s DawnNews reported.

But another spokesman, Mohammad Khurrassani, from the Pakistani Taliban’s central organization, disavowed any role..

We “strongly condemn the attack on Bacha Khan University in Charsadda and disown the attack, saying this is not according to Shariah,” Khurrassani said.

Wednesday was the 28th anniversary of the university’s founder, Abdul Ghaffar Khan — a 1920s Pashtun independence activist and pacifist also known as Bacha Khan. Guests were gathered at the university to pay tribute to the man when the militants came, said student Zahoor Khan.