A roving pack of robbers targeted University of Minnesota students four times on or near campus last weekend, punching and kicking their victims while stealing their valuables, authorities said.

The four attacks occurred between 1 and 4:45 a.m. Sunday at three locations: the intersection of Harvard Street and Washington Avenue; on Washington Avenue on a Metro Transit bus near the Willey Hall stop, and at the intersection of 17th Street and University Avenue near the Armory, according to university police.

In each instance, police said, two or more students were robbed of cash, wallets and cellphone, and suffered minor injuries from being punched or kicked. Descriptions of the young male suspects are limited. They appear to be 18 to 25 years old, according to police.

University police officials said they are coordinating their investigation with Minneapolis and Metro Transit police.

The suspects have been working in groups of up to six but as few as two, said campus police Deputy Chief Chuck Miner.

“We’re getting a few calls” from the public with leads, Miner added, but nothing that has led to any arrests.

Miner said his department will be adding “lots of extra personnel on the streets” in the coming days in an effort to halt the incidents and make arrests.

Even though the victims were not alone, “walking with someone is still the best and easiest way to ensure your safety late at night and on the weekends,” university police said in a campus alert.

Miner said that at least one victim was inebriated at the time, and “historically, that is a factor” in people making themselves vulnerable to attack.

“[But] weather is probably the biggest factor,” the deputy chief said. When it’s nice out, “the bad guys are out and the good guys are out, so to speak,” he said.

Anyone with information about these incidents is asked to call the university police at 612-624-2677.