CAMBRIDGE (CBS) – Cambridge police have issued a warning to residents after two violent robberies on city streets.

Both victims were women who were walking alone. In each case, a man held what may have been a knife to the victim’s neck and demanded money.

The incidents happened January 10 on First Street and on January 21 on Allston Street.

Both attacks happened between 7 p.m. and 10 p.m.

Police say they don’t know if the robberies are related.