BOSTON (CBS) — Police are asking residents of Dorchester and South Boston to be on alert after a reported sexual assault and armed robbery Sunday night.

Officers responded at 11 p.m. to the area of Dorchester Avenue and Harbor View Street, where the woman said she was robbed at knifepoint and then sexually assaulted.

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She described the attacker as a black man in his 20s with a medium build, short black curly hair, and a small amount of facial hair. He was wearing dark clothes and may have fled on foot toward Sydney Street, the woman said.

There have been three other attacks in that area since July.

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The reported assault came at a time when people might have been outside to watch the Supermoon Lunar Eclipse, and police are hoping someone might have spotted the attacker.

Authorities are urging residents to take safety precautions like not walking alone at night, and avoid distractions like cellphones.

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Anyone with information is asked to call police.