Twenty people were killed at a university in Pakistan today after a Taliban splinter group broke onto the grounds and opened fire.

In addition to the 20 fatalities, provincial Gov. Sardar Mehtab Ahmed Khan said that at least 50 other people had been injured in the attack at Bacha Khan University. Pakistani Army spokesman Gen. Asim Bajwa said that 18 students and two professors were killed.

Four shooters have also been killed, a Pakistani military source told ABC News.









What We Know About the Shooting

The attackers took advantage of heavy fog, cutting through barbed wire and then scaling the back wall of the university.

Witnesses said they saw the gunmen storm the rear entrance of the campus in Charsadda, Pakistan.







They fired indiscriminately, killing students in classrooms and dormitories where they were hiding after the gunfire erupted, according to witnesses and officials.

The local police chief reported that the attackers were wearing suicide vests and surviving students said the gunmen were using AK-47s.

The Pakistani military was able to move in quickly, and Gov. Khan said they have now secured the university.









Who Were the Attackers

Omar Mansoor, the leader of a Pakistani Taliban splinter group, has claimed responsibility for the attack.





How Have Officials Responded

A spokesman for the main Taliban faction in Pakistan has condemned the attack, according to The Associated Press.

Mohammad Khurasani, the spokesman, called the attack "un-Islamic" and insisted that the Pakistani Taliban was not responsible for the attack, the AP reported.

Pakistani Prime Minister Mawaz Sharif is in Switzerland for the World Economic Forum at Davos and issued a statement to Pakistan's government media: "Prime Minister Muhammad Nawaz Sharif is deeply grieved over the sad incident of terrorists' attack on Bacha Khan University, Charsada, which has reportedly resulted into the loss of precious human lives and injured many others. Issuing necessary directions to the law enforcement agencies for the earliest elimination of the terrorists, the Prime Minister is personally monitoring the situation and he is continuously informed on the measures taken to combat the terrorists."









School Targeted by This Group in the Past

This same splinter group is believed to have been responsible for another attack on a school in the same region of northwest Pakistan in 2014.

There were 130 people, mostly children, killed in that attack in Peshawar, making it the deadliest terror attack in Pakistan's history.

ABC News' Emily Knapp, Mustafa Hameed and Kelly Stevenson contributed to this report.