Two undergraduates were robbed at knifepoint by two assailants at 12:40 a.m. on Tuesday morning in front of 100 Walker St., which borders the Quad, according to a statement released by the Harvard University Police Department (HUPD) yesterday.

The two suspects, who are described by the HUPD as black males 18 to 20 years of age, have not been apprehended.

One of the victims, a Currier House resident, said the two assailants ran from Linnaean St. towards him and his friend, a Pforzheimer House resident.

"I thought it was friends of mine, and I thought it was a joke until I saw the knife," he said, speaking on the condition of anonymity.

"They were shaking, really scared," he said. "Basically, the guy put a knife to my belly. I couldn't see it, but definitely could feel it."

The assailants demanded money from the students and fled after the Currier House resident surrendered his wallet, according to the student.

HUPD Chief Francis D. "Bud" Riley said police are looking into a possible connection between this robbery and one that occurred Tuesday night near the Peabody School, at 44 Linnaean St.

"To the best of our knowledge these are unarmed robberies," Riley said, contradicting the Currier student's account.

"We have had detectives working with Cambridge [police]...to work on any connections," the chief said.

Police distributed an advisory around the campus to make students aware of the incident, said HUPD Spokesperson Peggy A. McNamara.

Riley said police are also taking extra security measures near the Quad.

"We have increased patrols in the area, distributed descriptions of the subjects to officers [and] we have plainclothes and uniformed detectives in that area," Riley said.

Nonetheless, Riley urged students to be careful.

"I give the same caution to students as always: be aware of what's going on around [you]. If you feel a sense of unease, you should use safety phones to contact university police," he said.

Quad students said they were surprised and concerned about the incident.