Police from four cities and towns in Greater Portland are investigating a string of robberies this week at gas stations and convenience stores that may be connected.

In each of the four incidents, a man entered with a mask covering his face, showed a handgun and demanded money. No one has been hurt, and no one has been arrested.

Portland police Lt. Robert Martin said the four departments met Friday to discuss the investigations and share information.

“We’re investigating it. They’re in close time frame. The only commonality is a white male with a gun. The clothing is different, but same MO,” Martin said. “Concealed face, robbing gas stations.”

The departments are not making public what was discussed at the meeting, Martin said Friday evening.

The latest robbery was reported Thursday night in Cumberland, where police said someone robbed the Irving gas station at 174 Main St. around 8:44 p.m.

In Falmouth, police were searching for a man who entered the Lil’ Mart store on Route 1 shortly after 8 p.m. Wednesday, showed a handgun and fled with an undisclosed amount of cash. Police described the robber as white, wearing a gray hooded sweatshirt, a face mask and black gloves.

Just before 1 p.m. Thursday, a white man entered the Good Things Variety store on Saco Street in Westbrook, showed a handgun, and robbed the store before running away.

Police used a dog to track the robber, but did not find him. He was described as about 5-foot-8, with a skinny to medium build, and wearing a blue sweatshirt or fleece vest with yellow lettering. A mask covered his face and he was wearing sunglasses.

Westbrook police Capt. Steven Goldberg issued a statement Thursday night, saying, “Part of the investigation will include determining if this robbery is linked to the recent robberies in Portland and Falmouth.”

In Portland on Tuesday night, a man with a silver handgun entered the Riverton Gas Station at 1585 Forest Ave. and demanded cash. He was described as about 30 years old, 5-foot-5 with a thin build. He was wearing a heavy dark jacket, a dark cap, dark gloves and a ski mask that covered half of his face.

Staff Writer Penelope Overton contributed to this report.