(CNN) -- Heavy clashes erupted between Iraqi security forces and gunmen who stormed a campus Saturday and used students as human shields, authorities said.
The majority of students were able to flee, but some are still inside al-Anbar University in Ramadi, police officials told CNN.
Approximately 1,200 students who live in the campus residential buildings were present during the attack; nearly 20 have been slightly injured, officials said.
Iraqi security forces have surrounded the university and are attempting to retake it from the attackers, who are believed to be Islamic State of Iraq and Syria (ISIS) members, police officials said.
Professors and other staff also live within the campus, police said.
ISIS is a Sunni Muslim extremist group formerly affiliated with al Qaeda.
The campus is about 110 kilometers (68 miles) west of Baghdad.