City police and officers at Pittsburgh's two largest university campuses are working together to crack down on a recent rash of street robberies.

There have been three late-night armed robberies since just after midnight Tuesday night.

Investigators believe the robberies were done by the same two suspects, both black males in their late teens or early to mid 20s.

At least one of the suspects was armed with a handgun in each robbery.

The most recent holdup occurred late Thursday night in Schenley Park, at Schenley and Frew streets near the campus of Carnegie Mellon University.

The first was reported at 12:27 a.m. Wednesday in the 300 block of Oakland Avenue.

One suspect held the victim at bay while the other rifled through the victim's pockets. The robbers took a wallet, cell phone, iPod, book bag and a laptop computer, police said.

The second incident was reported minutes later on Semple Street.

University of Pittsburgh police Chief Tim Delaney said a fourth incident was reported this week on Howe Street in Shadyside.

Though that incident didn't occur on either campus, the suspects' descriptions and the way they behaved were similar to the Oakland robberies, Chief Delaney said.

It appears the suspects may have access to a dark-colored vehicle as well, he said.

Police are also reviewing video surveillance from at least one of the crime locations.

Since the first robbery, the two college police departments have stepped up distribution of safety tips for students and staff on the campuses.

The fliers have been posted throughout Oakland, advising people to avoid walking alone, especially late at night. All of the robberies were reported between 8 p.m. and 2 a.m.

Students, staff and residents also are advised to be more aware of their surroundings, particularly during those high crime hours when strangers are approaching on the street.