Police are investigating a mugging outside Hartford Public High School Monday afternoon.

The robbery happened about 3:20 p.m. outside the school at 55 Forest St., Sgt. William Mooney said. A group of male teen-agers approached the male victim, and one punched him, Mooney said.

They stole his cell phone, he said.

The robbers ran away. They are described as 15-17 years old, about 5 feet 10 wearing a black, hooded sweatshirt and black pants.

Anyone with information is asked to call the Crime Stoppers tip line, 860-722-8477.