Two Dunkin’ Donuts shops — one in West Roxbury and another in Nashua, N.H. — were robbed Tuesday night by a white male suspect wearing black clothing that covered most of his body.

The two stickups were the 13th and 14th robberies of Dunkin’ Donuts locations in Southern New England since March. Thirteen have occurred in Eastern Massachusetts; the Nashua robbery was the only one out of state, occurring about 15 minutes north of the Massachusetts state line.

The first robbery was reported at about 7:15 p.m. Tuesday at the shop at 119 East Hollis St. in Nashua. The suspect entered the store brandishing a black semi-automatic handgun, forced an employee to empty a register, and fled on foot with an undetermined amount of cash, apparently jumping into a car a short distance away, said Nashua Police Lieutenant Denis Linehan.

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Linehan said he suspected the doughnut shop robber may have been involved in several other crimes in the Nashua area, including a street robbery in Hudson, N.H., also on Tuesday night.

Roughly an hour and a half after the first Dunkin’ robbery, at 8:45 p.m., Boston police received a report of another shop robbed at 1435 VFW Parkway in the West Roxbury section of Boston.

Witnesses told police that a male suspect walked into the shop brandishing a knife and forced employees to empty two cash registers. The suspect then took an undetermined amount of cash and fled on foot.

Police were hesitant to connect Tuesday night’s robberies — and have not made a definitive connection between any of the 14 robberies —but Linehan said “there would be enough time to get from Roxbury to Nashua” in the hour-and-a-half between the two crimes.

In all 14 Dunkin’ robberies the suspect has been covered in black clothing and identified as a white or Hispanic male. A black handgun was used in all of the robberies except the West Roxbury one.

No injuries were reported in any of the robberies.

Dunkin’ Donuts and Canton police increased their reward from $2,500 to $10,000 on Friday for information leading to the arrest of a suspect, according to Canton police, who are coordinating the investigation.

The company, which is headquartered in Canton, did not return calls seeking comment.