Given the ease with which gunmen reportedly scaled the low walls of Bacha Khan University, news agencies are pointing to the lapses in that effort.

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Pakistani villagers try to enter a local hospital where injured people were taken after the attack at Bacha Khan University. The Army said it had concluded operations to clear the campus six hours after the attack began, adding that four gunmen were killed.

There was no immediate claim of responsibility for the attack which came a little more than a year after Taliban militants killed more than 130 students at a school in Peshawar.

Speaking after today's attack, Prime Minister Nawaz Sharif said: "We are determined and resolved in our commitment to wipe out the menace of terrorism from our homeland".

"There was no announced threat but we had already beefed up security at the university".

Firing could be heard from inside the university where students, teachers and administration staff are present, say Pakistani media reports.

Mansoor, who was the mastermind behind the Peshawar school attack, said a four-man Taliban team carried out the assault.

"The death toll in the terrorist attack has risen to 21", regional police chief Saeed Wazir said without specifying if that included the four militants the army stated it had killed.

According to some reports two explosions were heard inside the university.

One faction of the Pakistan Taliban, the Dara Adma Khel splinter group, claimed responsibility for the attack. Provincial Minister Shaukat Yousafzai has confirmed that 25 people, including Chairman of Chemistry Department Professor Hamid a professor, have been killed and around 50 others injured in the terrorist attack.

The university has over 3,000 enrolled students and was hosting an additional 600 visitors on Wednesday for a poetry recital on the death anniversary of the Pashtun activist Abdul Ghaffar "Bacha" Khan, the university's vice chancellor said.

Military spokesman Major-General Asim Bajwa said on Twitter that two attackers had been killed.

Pervez said that the militants can not frighten Pakistani nation. On Tuesday, parents throughout northwestern Pakistan rushed to pull their children out of school after rumors spread through communities that a terrorist attack on a school may be imminent.