Nassau police are stepping up patrols following a violent robbery at a 7-Eleven in Old Bethpage.

Investigators say a masked man wielding a hunting knife held up the store on Old Bethpage Road early Sunday morning. After the suspect stole money from the store's two registers, authorities say he slashed the clerk in the face and hands.

Police are concerned that the violence came after the proceeds were already obtained by the suspect.

"It seems to be an act that was unprovoked by the victim at least at this point, and that gives rise that the individual who was committing this robbery, for some reason, he just wanted to hurt this individual," says Nassau Police Chief Steven Skyrnecki.

Officers spent the day visiting other 7-Eleven shops and convenience stores to speak with employees and review their security measures. They are reminding clerks about the importance of good lighting and functioning surveillance systems, and urging them to keep more than one person working the floor at all times.

Police are looking into whether the store that was targeted by the robber had working security cameras, but would not comment further.

Anyone with information on the robbery is urged to call Crime Stoppers at 800-244-TIPS.