Osman & Joe's Steak 'n Egg Kitchen along Wisconsin Avenue in Northwest D.C. has been robbed twice in the last month. (Bill O'Leary/The Washington Post)

Two masked men, one armed with a handgun, robbed an all-night diner near the Tenleytown Metro station in the District early Monday and fled with money from a cash register, police said.

One man urged his accomplice to “shoot them then, just shoot them” when three employees of Osman & Joe’s Steak ’n Egg Kitchen said they could not open the safe, a police report said. One of the men slapped a customer who reached for a cellphone.

The robbers — who entered through a back door while deliveries were being made and employees were conducting inventory — took money from the register and a purse, police said.

No serious injuries were reported in the holdup, which occurred about 3 a.m. There were three customers and three employees in the restaurant, a small white house with a white picket fence in the 4700 block of Wisconsin Avenue NW, on the border between Friendship Heights and Tenleytown.

The manager, Justin Anderson, said he will not let the robbery deter him. “We will continue to be open,” he said in an interview Monday morning. He said the robbers left in a white car with black rims and that he thinks surveillance cameras recorded the men before they donned their masks.

[At Steak ‘n Egg, prime real estate is always paramount]

Monday’s robbery was the second at the diner in a month. On Sept. 27, two men stole between $2,000 and $4,000 from a cash register and a safe, as well as a cellphone, police said.

In that case, police said a gunman pushed a customer who resisted giving up his cellphone and fired at him. The shots missed, police said, and the robbers fled in a brown SUV with a gray bumper and Maryland license plates. That robbery occurred about 2:30 a.m.

Police did not say whether they think the holdups are related.

Anderson said that after the September robbery, the restaurant stopped accepting cash at night, and he thinks the robbers on Monday “couldn’t have gotten more than $200” from the register. He also thinks the robbers might have heard about the September holdup.

“I think it’s related in that it’s word-of-mouth on the street,” Anderson said. “The robbers got a big payout the first time, and these two guys probably heard there’s a lot of money at Steak ’n Egg. But we don’t do cash anymore at night.”

He added: “A stupid robbery.”