Chicago police are alerting residents of the city's Logan Square and Palmer Square neighborhoods of recent sexual assaults.

In each of the assaults, a man approaches women from behind, either on the sidewalk or in the hallway of apartment buildings, and assaults them. In two cases he was armed with a sharp object, police say.

The most recent sexual assault against a female victim happened early Sunday in Logan Square, and two others happened last month in the Palmer Square area of the neighborhood, Chicago police said.