BERKELEY, Calif. -- Berkeley police are warning residents to keep their doors and windows locked following a series of sexual assaults in the past few weeks.

There have been three incidents since June 17th, taking place inside homes on Milvia and Derby Streets, police say.

The most recent attack happened Tuesday morning around the corner from Milvia Street. A man armed with a weapon entered a woman's home at about 4:30 a.m. and sexually assaulted her, police said.

This attack was similar to two other incidents in the past few weeks and police say they are worried the assaults may be related and that the assailant may strike again.

With this in mind, police are reaching out to the public in an effort to keep people safe and possibly stop another attack from happening.

"We are very concerned there may be another crime," Berkeley Police Sgt. Mary Kusmiss told KTVU. "That's why we're really reaching out and urging the community to take crime prevention measures but also to call us about any suspicious people or activity."

Berkeley Police say they typically see about two stranger sexual assaults a year in the city and they say three incidents in a matter of weeks is very unusual.

Residents who live near the recent attacks say they are worried for their safety.

"It's very scary," Berkeley resident Doug Jackson told KTVU. "I have a daughter who lives with us and it's one of those things where we're concerned."

Police stress that importance of keeping homes secure, even in the hot weather. They say keeping windows open to stay cool could provide easy access for a dangerous criminal.

"We're really stressing if you can secure and lock your doors even in spite of the weather, that's one of the best crime prevention measures you can take," Kusmiss said.

Police have a vague description of the suspect. They say he's an African-American man in his late teens or early 20s with a thin but muscular build.

Forensic evidence has been collected from the crime scenes, which police say could possibly lead them to the assailant.