Two students were shot dead and four others were injured in separate campus shootings in Texas and Arizona, the latest in a string of gun-related incidents in the US.
The shootings occurred just a week after 10 people were killed when a gunman entered his class at Umpqua Community College in Roseburg, Oregon, and began shooting his classmates and professor.
Early Friday, an 18-year-old student shot one student dead and wounded three others in Northern Arizona University (NAU) in Flagstaff, Arizona.
Authorities identified the suspect as Steven Jones, a freshman at NAU, who pulled a handgun in a confrontation with students, Reuters reported. The shooting happened in a parking lot of the Flagstaff campus and the shots were reported at 1:20 a.m., the university said.
The fatality was identified as student Colin Brough and the injured were Nicholas Prato, Kyle Zientek and Nicholas Piring, who suffered multiple gunshot wounds and were being treated at Flagstaff Medical Center.
The shooting happened just hours before President Barack Obama was to visit Roseburg, Oregon, to meet families of the nine persons killed in a mass shooting at Umpqua Community College last week.
Brough, Piring and Zientek were listed as business students of the university and had links to Delta Chi fraternity.
Delta Chi confirmed to KPXN-TX that frat members were involved in the shooting but said the shooting "had no ties to the chapter."
Jones was arrested by university police and is cooperating.
Police said guns are barred in the university campus under Arizona law and Arizona Board of Regents policy.
University president Rita Cheng said classes were to go on as scheduled on Friday and branded the incident as "isolated," adding that "our hearts are heavy."
Obama vowed to step up efforts to curb gun violence after the Oregon shooting.
At Texas Southern University in Houston, one person was also killed while another was wounded in a shooting at an apartment complex adjacent to the campus just hours after the Arizona incident.
Two suspects were arrested.
The university was placed on lockdown for several hours after the shooting and classes were cancelled.
The identities of the suspects and the victims have not been released.