Nassau police are investigating the holdup Thursday of an East Meadow delicatessen by a masked gunman as part of a string of at least seven armed robberies.

"We're not sure if it's one individual, but we're investigating these as a pattern," a police spokeswoman said Friday.

Shortly before midnight Thursday, a man wearing a black mask entered the Route 24 Deli at 1820 Hempstead Tpke. and demanded cash at gunpoint, police said.

The clerk handed over an unspecified amount of cash, and the suspect fled on foot. Two employees were in the store at the time, police said.

Three of the robberies that fit the pattern, according to police, happened on April 30, when a convenience store in Merrick and 7-Elevens in Baldwin and West Hempstead were held up.

On April 15, three other stores -- a grocery store in Freeport and 7-Elevens in Valley Stream and East Meadow -- were robbed.

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Police on Thursday released a photograph of the suspect in the April 15 East Meadow robbery; the gunman entered the 7-Eleven at 2138 Hempstead Tpke. at 4:42 a.m., police said.

In all but one of the robberies, the stores were hit by a masked gunman wearing dark clothing, according to police.

In the West Hempstead incident , two men robbed the 7-Eleven gas station store in the 800 block of Hempstead Turnpike, wearing a mask and black hoodie, police said. Only one of the men was armed.

No injuries were reported in the robberies, police said.

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