Hours after Nassau County police released a video of a knife-wielding masked man suspected in a series of robberies, they think he struck again, knocking off a Carvel ice cream store in North Valley Stream on Tuesday night.

Nassau Det. Lt. Richard LeBrun said the man responsible for the robberies wields a kitchen knife that is 6 to 7 inches long.

“He demands cash, he flees,” LeBrun said at a news conference at Nassau police headquarters on Wednesday.

He said police are dedicating a large number of resources to catching the robber, including members of the bureau of special operations and the criminal intelligence rapid response team.

“We’re all on heightened alert. We’re intensifying our patrols around the areas” where the robber has struck, LeBrun said.

He said the businesses hit were probably attractive targets to the robber because they are open late and have glass fronts, which allowed the thief to see inside.

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That describes the Carvel at 1551 Dutch Broadway, one of nine places the man has hit over a six-week span, police said. It was robbed Tuesday about 9:30 p.m. and Major Case Bureau detectives said they are investigating.

Police released video Tuesday afternoon of what they believe is the first robbery, at a New Hyde Park Dunkin’ Donuts shop on March 1.

In the Carvel robbery the man had a 6-inch knife and walked around the counter, demanding the clerk open a register, police said.

The suspect took an unspecified amount of cash and left, fleeing east on Dutch Broadway. The clerk was the lone employee and was not hurt, according to a news release.

The man was about 6 feet tall and wore a black hooded shirt, jeans, tan work boots, black gloves and dark glasses.

In previous robberies, the man was similarly described, including being between 25 and 30 years old and weighing about 170 pounds.

Police said the man in the video also had robbed a 7-Eleven in Bethpage, a Subway sandwich shop in North Merrick and five other Dunkin’ Donuts stores — two in Plainview, one in East Meadow, one in Oceanside and one in Massapequa Park.

On Monday morning, police said they were trying to determine if the suspect also was responsible for the robbery of a Williston Park Dunkin’ Donuts on April 8.

They have since ruled out his involvement, noting that the suspects’ descriptions did not match, police said.

Anyone with information can call Crime Stoppers at 800-244-8477. All information will be kept confidential.

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With Rachel Uda