PORTLAND — Portland police are looking for a bicycle-riding purse snatcher who has now struck twice in the past week.

A 54-year-old woman told police she was at Oak and Free streets talking on her cell phone near her car when a man rode up on a bicycle and grabbed her purse off her shoulder, police said.

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The force of the encounter knocked her to the ground, but she was not injured, police said. The man was wearing black clothing with a dark-hooded sweatshirt and riding a black bicycle, she said.

It is the second such incident in a week. On Sunday, a Scarborough woman told police that at 8:30 p.m. she was walking on the sidewalk in front of 145 Commercial St. when a cyclist rode past her and grabbed her purse.

Her male friend tried to chase the robber, but he got away, police said.

Anyone with information is asked to call 874-8533.