BOSTON -- Massachusetts State Police are investigating an assault on a woman at Nahant Beach Thursday night.

A 24-year-old woman was walking along the beach's paved walkway when she was attacked from behind on the stretch of pavement between the Ward and Nahant Bathhouses. Police said her assailant dragged her into dunes next to the walkway, near some concrete picnic tables, and sexually assaulted her.

The victim fought back and was able to break free and run away. She lost sight of the man after she fled.

The assailant is described as a dark-skinned man, who is about 6 feet tall and has a thin build. He was wearing a gray hooded sweatshirt with the sleeves rolled up, dark pants and a black baseball cap.

Anyone with information is urged to call the State Police Barracks in Revere at 781-284-0038.