The Pakistani military has announced the detention of five men on suspicion of facilitating a deadly attack on a university in the country's restive northwest.

On January 20, four gunmen attacked Bacha Khan University campus in Charsadda District in Khyber Pakhtunkhwa Province, killing more than 20 people. Pro-Taliban militants later claimed responsibility for the assault.

Military spokesman Lieutenant General Asim Bajwa told a televised press conference in the city of Peshawar on Saturday that authorities have arrested five suspects. “Another one, whom I will call terrorist-A is still at large.”

“Terrorist-A” is said to have arranged transportation for the four gunmen from the town of Torkhum near the border with Afghanistan. The men are accused of providing accommodation for the attackers and giving them a rickshaw that they used on the day of the raid.

The detainees also helped the attackers buy their weapons in the country's tribal belt.

One of the accused, who is a laborer, had reportedly done some masonry work in the university several days before the attack and made a map of the place which he gave to the assailants.

Elsewhere in his comments, the Pakistani military spokesman said authorities believe the attack on the college was masterminded and controlled by a Pakistani Taliban militant residing in Afghanistan, identified as Umar Mansoor, who is also held responsible for a massacre in December 2014 in which 134 children were killed in Peshawar.

“The attackers were prepared in Afghanistan,” Bajwa said, adding, “We have come to the conclusion that terrorism cannot be fought when there are accomplices and facilitators.”

The pro-Taliban faction behind the attack at Bacha Khan University posted video footage on Friday in which the militants promised more attacks on schools and universities throughout the country.

Pakistan has been facing security challenges since it joined an alliance with the US in the so-called war on terror in 2001. Thousands of people have been killed over the past years as a result of a surge in violence in the country.