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.

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.