A 44-year-old Leesburg area woman was sexually assaulted early Tuesday while working at the 7-Eleven on Plaza Street, Leesburg police said.

The woman was the only clerk in the store at 22 Plaza St. NE when a man entered shortly before 2 a.m. and walked around as if he were shopping, according to Capt. Clagett Moxley. The man then approached the clerk, threatened her with what police said was a "sharp instrument" and demanded money.

Moxley said the clerk handed over an undisclosed amount of cash before the man "brutally" assaulted her. Before fleeing, the assailant struck the woman on the head with an unknown object.

The woman, who suffered bruises and a cut on her head, was treated at Loudoun Hospital Center and released. Moxley said detectives are reviewing a video from a store's surveillance camera to see whether the suspect has been caught on film.

Margaret Chabris, a spokeswoman for Dallas-based 7-Eleven Inc., said that the convenience stores generally have two employees on duty during the overnight shift and that a second employee had been scheduled to work at the Plaza Street store. That person had worked an earlier shift at the Purcellville 7-Eleven and had to stay there because another employee failed to show up for work, Chabris said.

She said the clerk at the Leesburg store had called a manager, who was on his way in when the assault took place. The store is just down the street from the Leesburg police station.

The assailant is described as a black male about 5 feet 9 inches tall, police said. He was wearing black pants and a black sweat shirt.