In separate incidents, attackers have opened fire at two US universities, each killing a person in Arizona and Texas. The shootings happened the same day the US president visited victims of a college shooting last week.
Texas Southern University was placed on lockdown on Friday with classes cancelled after a shooting occurred at a Houston apartment complex owned by the university. One person was killed and another wounded.
Houston police said a possible suspect has been detained. It was unclear if any of the people involved were students.
Earlier on Friday, an attacker opened fire during a fight between two groups of students at Northern Arizona University, police said. The 18-year-old suspected gunman was captured and taken to custody.
At least one person was killed and three more wounded in a shooting at Northern Arizona University (NAU) in Flagstaff, campus authorities said.
"This is not going to be a normal day at NAU," school president Rita Cheng said. "Our hearts are heavy."
Police identified the suspect as an 18-year-old, believed to be a freshman in Flagstaff school. All three victims were also students at the university.
The incident began as a fight between two groups of students in front of a dorm, police said.
Student Maria Gonzalez told the AP news agency that she heard the gunshots early on Friday, but believed them to be firecrackers.
"I was studying for an exam so I looked out the window and see two people running, and that's when I realized they weren't fireworks they were actually gunshots," she said.
The Flagstaff campus, some 230 kilometers (155 miles) north of Phoenix, has more than 25,000 undergraduates.
This is only the latest public gun-related incident in the US, coming during a fierce debate about gun safety in American society.
Obama in Oregon
President Barack Obama met privately for an hour on Friday with families of victims of a mass shooting at a community college in Oregon. He told reporters afterward that the United States had to figure out how to stop these shootings from happening.
"I've obviously got strong feelings about this," Obama said. "We're going to have to come together as a country, but today is about the families."
Nine people were killed in the shooting last week at Umpqua Community College in Roseburg, Oregon.
About 250 gun rights activists had gathered at the airport carrying signs saying, "Obama Go Home." Many people in Roseburg have expressed anger at Obama's call for stricter gun control laws.
"By coming here, Obama is going to politicize a tragedy by saying that you have to have gun control," George Starr told the AP news agency. "It's not that we are bloodthirsty, it's that we want to protect ourselves and our families."
Obama admitted to politicizing the issue last week during a White House press conference.
"I will politicize it, because our inaction is a political decision that we are making," he said.
According to the Everytown Gun Safety advocacy group, there have been at least 144 school shootings in the United States since 2013 - an average of nearly one per week.
sms/jm (AP, AFP, dpa, Reuters)