"This is very concerning for us," said RCMP Sgt. Drew Grainger after the incident just after midnight Saturday at the Vancouver campus.
UPDATE: The UBC RCMP suspect a single person is behind a series of sex assaults at UBC, Global News reported.
"We are engaged with many partner law enforcement agencies to attempt to identify and apprehend the person or persons responsible for these attacks."
A 17-year-old student was walking alone to her residence when a man suddenly emerged from a wooded area, Grainger said.
The attacker put his hands around the teen's hips, tried to drag her into the woods and punched her in the face, he said, adding the girl sustained a black eye.
"She's shaken up. It was a traumatic event for her and thank goodness she wasn't hurt more than she was."
The man also ripped at the girl's clothes but ran off when she screamed for help, Grainger said.
The suspect has been described as a tall, thin man in his late 20s to early 30s, with a possible American accent.
"He put his hand over her mouth and told her to be quiet," Grainger said.
Last Sunday, a 20-year-old woman was assaulted as she returned to her UBC apartment at about 3:30 a.m. On Sept. 28, a 19-year woman fled after a man grabbed her from behind at 2:45 a.m.
In each case, the women were attacked from behind on a Friday or Saturday night by a Caucasian man wearing a dark hoodie, Grainger said.
Police are calling on students to not put themselves in a vulnerable position by walking alone late at night.
"We're warning all citizens of the campus area to think twice about moving around at that time of night and to think about the buddy system."
Students can also call campus security if they find themselves having to walk home late at night.
After the second incident, RCMP asked student housing officials to educate residents about safety issues, Grainger said.
"Student housing is putting on little meetings for the residents of the campus to provide information on how to protect yourself ... to try and prevent other incidents like this from happening."