By George P. Hassett A woman walking home from the Porter Square train station was knocked to the ground and attacked by a man on Sunday night, police said. Police are looking for a suspect described as a white male, 20 to 25 years old, 5 feet 6 inches tall, medium build, brown hair and clean shaven.

The woman told police she was able to pepper spray the man after he attacked her around Summer and Belmont streets and he fled the area.

"Somerville Police have increased patrols in this area and have shared this information with other Police Departments. Although we believe this to be an isolated incident, we want to alert residents, especially women, who may be walking in this area, to be especially vigilant. We encourage women to take common sense precautions, be aware of their surroundings and avoid distractions such as headphones and Ipods. If you carry a cell phone, keep it in an easily accessible place," Deputy Chief Paul Upton said in a phone alert sent to Somerville residents.

The Somerville Police Department is working jointly with other police agencies to identify and apprehend this suspect as quickly as possible. The incident is not believed to be connected to earlier indecent assaults in the city, police said.

Police are asking citizens to call 911 if they see anyone who is acting suspicious in the area.