DENVER -- Sporting a camouflage jacket and dark reflective glasses, a bank robber threatened a Wells Fargo teller with what appeared to be a hand grenade before taking off with cash in the middle of the afternoon, Boulder police said.

About six customers were inside the Wells Fargo bank in the 3300 block of 30th Street when the man robbed it around 3 p.m. Monday, police said.

The teller told police the robber walked up to the counter before asking for money, and then took off with an unknown amount of cash.

He is described as a white man in his late 40s to early 50s, about 5 feet 8 inches tall, with a scruffy face and a large, round nose.

Police said he was wearing a baseball cap, dark glasses, a camouflage jacket and blue jeans at the time of the robbery.

The FBI is helping Boulder police in the investigation. Boulder police released surveillance photos of the robber.

Anyone with information about the robbery is asked to contact the Boulder Police Department at 303-441-3330, or anonymous tips can be made at 1-800-222-TIPS.

A $1,000 reward is being offered by Boulder County Crime Stoppers to anyone with information that leads to an arrest and filing of charges in the case.