BROOKLYN - Police say a woman was robbed at knife-point on the subway in Brooklyn, and now they're trying to track down the attacker.

Investigators say the incident happened yesterday morning on a southbound F train by the Fort Hamilton Parkway station. Police say the suspect put his hand around the woman's throat and showed a knife before taking her purse and cell phone. He also demanded the victim remove her underwear, although she was not sexually assaulted, police say.

The man was captured on video fleeing the train platform. Police have released a sketch of the suspect, whom they describe as a bald, black male, about 45-50 years old. They say he's about 5'10" tall and stocky, weighing about 200 pounds.

Investigators say the suspect is not the same person wanted for a rash of sex assaults in Park Slope and Sunset Park.

Police are urging anyone with information to call Crime Stoppers at 1-800-577-TIPS.