The Taliban claimed responsibility for a school shooting in northwestern Pakistan that left at least 19 people dead.

The Associated Press reported Wednesday morning the death toll could be as high as 30, though such figures cannot be considered official at this time. Four gunmen entered Bacha Khan University, opening fire on students and faculty, before they died in a firefight with police and military personnel.

Tehrik-i-Taliban Pakistan, the nation's Taliban faction, is known for targeting education institutions for their attacks, according to The New York Times. The Bacha Khan attack occurred 13 months after the group massacred an army school in Peshawar about 35 kilometers away, killing 150 people.

Pakistan Prime Minister Nawaz Sharif released a strongly worded statement referring to the attackers as "cowards" and calling for the nation to mount a "ruthless response," The Washington Post reported. The newspaper and other news outlets reported some people were shot in the head execution style.

"I saw two terrorists standing on the roof... They were shouting 'Allahu Akhbar,'" Basit Khan, a computer science student, told The Post. "After that, firing started and I and my friends started running. There were people screaming. We were terrified."

Since the Peshawar attack, Pakistan renewed and strengthened its fight against terrorism, The AP noted. The country lifted its moratorium on the death penalty and hanged four people found to be involved in the massacre a year after it occurred.

David Hale, the United States' ambassador to Pakistan, released a statement on the shooting as well.

"I strongly condemn today's appalling attack on Bacha Khan University in Charsadda. The blatant disregard for human life displayed by these attackers is intolerable. It is especially reprehensible that the attackers targeted an educational institution where students and educators are seeking to better themselves and the nation of Pakistan," he said. "This attack stands in stark opposition to the desires of the Pakistani people to create a secure, stable, and prosperous country, based on respect for all. We offer our deepest condolences to the victims and their families during this time of grief.

"The United States stands with the government and people of Pakistan and is committed to supporting their efforts to fight terrorism. We support Pakistan's efforts to bring to justice those behind the attack."