Four people remained hospitalized in fair condition on Tuesday after a car and knife attack by an Ohio State University student that was being investigated as a possible terror attack, officials said.

The student, Somali immigrant Abdul Razak Ali Artan, drove a car into a group of people on Monday morning at the school's Columbus campus, then stabbed several others with a butcher knife before he was shot and killed by a police officer, authorities said.

A U.S. official, who asked not to be named because of an ongoing investigation, told Reuters that U.S. agencies were investigating the attacker's background and motives, but could say yet whether he had any ties to suspected militant cells or groups.

Artan, an 18-year-old immigrant from Somalia, was a legal permanent resident of the United States, two other U.S. government sources said. He may have been as old as 20, according to Ohio State University Police Chief Craig Stone.

U.S. Representative Adam Schiff, the ranking Democrat on the House Permanent Select Committee on Intelligence, said on Monday that intelligence agencies were assisting in the investigation.

"It bears all of the hallmarks of a terror attack carried out by someone who may have been self-radicalized," Schiff said in a statement.

The attack injured 11 people, one of them critically, Columbus fire officials said.

Two people remained hospitalized at Ohio State University Wexner Medical Center, a spokeswoman said on Tuesday. Two others were at Riverside Methodist Hospital, according to a spokesman. Seven people were released, they said.

A spokesman for Columbus' Somali community denounced the attack.

"I want everyone to know that we the Somali-American community stand shoulder-to-shoulder with our fellow Americans in condemning the sickening violence that took place in our city earlier today," Abdi Dini, a member of the Somali community, told a news conference in Ohio on Monday.

With nearly 60,000 students, the Columbus campus is the state's flagship public university.