Chapel Hill, N.C. — The University of North Carolina at Chapel Hill has reported a second strong-arm robbery on its north campus this month.

University police said that shortly after midnight, Gael Chatelain, 24, and Nadia Chatelain, 26, were walking west between Hill Hall and the Smith Building, between Franklin Street and East Cameron Avenue.

Gael Chatelain told police that the robber grabbed him from behind and pushed him to the ground. Gael Chatelain said the robber kept assaulting him and asked for his ATM card only at the end.

In about 20 seconds, Gael Chatelain said he was punched and kicked more than a dozen times before a public-safety officer on a routine foot patrol responded to the attack. The officer confronted the robber and drew his gun, and the robber fled the scene, Gael Chatelain said.

Police said that no weapons were used in the robbery.

The victims, both from Orange County, are siblings; Nadia Chatelain graduated from UNC, and Gael Chatelain is an alumnus of North Carolina State University.

Gael Chatelain said he had returned home this week from a long trip to Africa.

Officers described the robber as a black man in his early to mid 20s, 5-feet-8 inches tall, with a medium build. He wore dark jeans and a dark, possibly navy blue T-shirt.

Officers said it would be premature to link Saturday's robbery with a July 12 strong-arm robbery, also on the north campus, at this point in the investigation.

Police issued a similar suspect description for one of two men involved in the earlier robbery outside Morehead Planetarium, in the 200 block of Franklin Street. The 23-year-old victim told police the robbers struck him from behind and knocked him to the ground before fleeing with his wallet.

University police warned the campus community to take extra safety precautions after Saturday's robbery.

Some people on campus expressed concern about the cases.

“It does concern you as a parent," said Laurie Jonsson, who was visiting campus with her daughter from Washington state. "You want to make sure your kids are in a school that’s safe."

UNC graduate student Brewer Heath said people on campus are on  “high alert."

Lucy Barrios, a UNC law student, said she is taking safety precautions, but there is only so much she can do.

“You can’t really drive around campus, especially like to Franklin Street, which is where I always go. So if you need to go someplace at night, it’s just easier to walk,” Barrios said.

Anyone with information about Saturday’s robbery was asked to call university police at 919-962-8100 or Chapel Hill-Carrboro-UNC Crime Stoppers at 919-942-7515. All conversations are confidential; no one must identify themselves or appear in court.