ISLAMABAD: The Foreign Office on Monday summoned the Afghan Charge d'Affaires, Syed Abdul Nasir Yousafi, to convey Pakistan's concern regarding the use of Afghan soil by terrorist elements in the Bacha Khan University attack, said a statement issued from the FO.

It said the diplomat was summoned on Monday and was told that investigations revealed the perpetrators of the deadly attack on the varsity were operating from Afghan territory and used the Afghan telecommunication network.

Related: APS mastermind claims Bacha Khan University attack, 21 killed

The statement further said relevant evidence had also been shared with the Afghan diplomat. It was conveyed to the Afghan government that they must take action against the perpetrators of the terrorist attack and extend cooperation to Pakistani authorities in order to bring them to justice, it added.

At least 21 people were killed when unidentified gunmen entered the university in Charsadda town last week and opened fire on students and faculty members.

The mastermind of the APS Peshawar attack, Umar Mansoor, of the banned Tehreek-i-Taliban Pakistan (TTP) Geedar group claimed the attack through a post on his Facebook page, adding that four attackers were sent to the university.

Related: Afghanistan should act against elements plotting terror in Pakistan: PM

Authorities say the Bacha Khan University attack was planned and orchestrated by Pakistani Taliban militants based in neighbouring Afghanistan, and called on the Afghan government to co-operate in its investigation.

Five suspects have so far been arrested for acting as “facilitators” to the attack, Pakistan Army's media wing said Saturday.

Pakistan Army has been leading a ground and air operation against militants in the country's tribal areas since June 2014. The military claims as a result of its operation, which it says has seen phenomenal success, several terrorists have crossed the border into Afghanistan, from where they are now operating.

Last year, at least 13 terrorists attacked a Pakistan Air Force (PAF) camp in Peshawar's Badaber area leaving at least 42 people, including the attackers, dead. TTP spokesperson Muhammad Khorasani had claimed responsibility for the attack in an e-mail sent to journalists.

The DG ISPR had back then also claimed that the Badaber attack was planned and controlled from Afghanistan.

Both countries blame each other for harbouring Taliban fighters active on both sides of their 2,400 kilometre (1,500 mile) border, fanning distrust between Kabul and Islamabad, and complicating a peace process in Afghanistan.