An unknown attacker sexually assaulted a female undergraduate in a Yard dorm early Thursday morning, according to the Harvard University Police Department (HUPD).

The victim described her attacker as a six foot tall white male with crew-cut hair. No further description was available.

"We have no reason to believe the attacker was an insider and we have no reason to believe the attacker was an outsider," HUPD Chief Francis D. "Bud" Riley said.

There are no suspects at this time, he said.

The attack, which occurred around 4:30 a.m., was reported to police within an hour.

Because the victim filed a police report on the condition of anonymity, Riley declined to release the location or specific circumstances of the attack.

HUPD issued a community advisory on Friday morning after discussions with the victim.

Riley warned students to be aware of any suspicious activity in their dorms and reminded them to lock their doors.

At this time, police say they believe the door to the room where the attack occurred was unlocked.

Anyone with information regarding the attack is asked to contact HUPD's criminal investigations unit at 617-495-1796.

--Staff writer Garrett M. Graff can be reached at ggraff@fas.harvard.edu.