Police are investigating an armed robbery that happened Wednesday night at the Xtra Mart convenience store on Brighton Avenue.

Sgt. Joe Ezepek said a man walked into the store around 6:15 p.m. with a ski mask over his face, waved a butcher knife at the clerk and demanded money.

The clerk handed over the cash drawer to the robber. Ezepek said the suspect walked out of the store with an undetermined amount of cash and went to the rear of the building, where he fled in a white pickup truck. Ezepek said police have been unable to determine the make and model from the surveillance video.

Police are describing the robber as a white man. He was wearing a ski mask, a blue coat, faded jeans and work boots. Anyone with information about the robbery is asked to contact Portland police at 874-8575.