Beacon Hill residents were on edge Sunday, a day after a woman was sexually assaulted and robbed inside her apartment in the neighborhood, while police urged the public to be vigilant after that attack and two assaults of teenage girls in Roxbury last week.

“It’s sort of nerve wracking, because I always thought of this as a safe neighborhood,” said Julia Probert, 23, as she walked with friends on Sunday afternoon near the scene of the Beacon Hill attack. It occurred on Saturday at about 3:15 a.m. near the corner of Joy and Myrtle streets, where stately brick homes are located close to shops and a public playground.

Like other residents, Probert said she plans to be more aware of her surroundings.

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Paul Szetela, 61, said he was shocked to learn of the attack.

“It’s kind of a quiet neighborhood,” Szetela said. “You don’t expect that kind of thing. It’s pretty sad, and I’ll be warning a lot of the single women that live in this neighborhood about what’s going on.”

According to police, a man forced his way into the woman’s apartment and brandished a weapon that may have been a knife before assaulting and robbing her. Police have not identified the woman, who is in her 20s, but said Sunday that she did not know her attacker.

Boston Police Deputy Superintendent Kelly Nee said during a news conference at police headquarters that investigators do not believe the Beacon Hill assault is related to the Roxbury cases.

If attacked, Nee said, residents should shout as the victims in Roxbury did on Monday and Tuesday evenings.

“They screamed and they were able to prevent the assault from getting any further,” she said. “So yelling, ‘Fire,’ ‘Help,’ ‘Rape’ – anything like that – scream. It’s a way of drawing attention to yourself and alerting people that you need help.”

Near the Beacon Hill intersection on Sunday afternoon, neighborhood residents were unsettled by the news.

“It’s kind of scary because you think it’s a safe neighborhood,” said Meaghan Elliott, 26. “There are people walking around at all times of day.”

A similar attack occurred on Joy Street in November 2004, when a 16-year-old boy forced a woman into her apartment and raped her repeatedly at gunpoint.

Police have released an ATM surveillance photo of a suspect in Saturday’s attack. The woman described her assailant as a black male in his late 20s to early 30s with braided hair and a medium complexion, wearing a du-rag type head covering, a tan three-quarter-length construction jacket, dark jeans, and dark sneakers. He was believed to be carrying a large blue backpack.

According to preliminary crime statistics from Boston police, through Nov. 5 there had been 234 reported rapes or attempted rapes in the city, up from 221 at this time last year.

There were 18 reported or attempted rapes through Nov. 5 in the police district that includes Beacon Hill, compared to 17 at the same time last year. There were 48 such reports in the district that includes Roxbury though Nov. 5, compared to 34 at the same time in 2011.

The two teenage girls were assaulted on or near Camden Street in Roxbury on Monday and on Tuesday.

Police believe the same suspect, described alternately as a baby-faced Hispanic male in his late teens and a non-Hispanic black with a Haitian accent and a medium build, may have committed both assaults. Both victims fought off their attackers.

Near the scene of the Beacon Hill attack, Rose Parsons, 53, a cashier at Beacon Capitol Market, said Sunday that the news caught him off guard, even though Saturday’s assault is not without precedent.

“I was really surprised,” he said. “Over the years we’ve had a couple of incidents, but it is a little disturbing.”

Nee said Sunday that whistles can be helpful in warding off an assailant and calling for help.

Helen Sulkowski, another neighborhood resident, said while she was walking her dog that she got a whistle after the 2004 case. She pulled a key ring out of her pocket to display the attached blue whistle.

“It’s scary,” Sulkowski said. “It is.”