LAWRENCE, Mass. (WHDH) -- Cab drivers in Lawrence said they are afraid for their safety following several armed robberies in the last month.

A number of cab drivers met at City Hall Tuesday to voice their concerns.

Police said there have been four attempted robberies this month alone and authorities described the situations as violent. In one case, the driver was pistol whipped. In another case, a gun was held to the driver’s head, according to police.

Some suspects have gotten away with cash, and in one case, a GPS.

Investigators said the robberies are happening in the Brook Street area. More officers have been assigned to that part of the city.

“It appears there is a group that’s targeting the cab drivers in that particular area. And they’re easy targets in the sense that they work all hours of the day and night, early morning. They have money ‘cause they have to make change. So, from time to time we see a pattern developing,” said Chief John Romero, Lawrence Police Department.

Officers were issued a bulletin detailing the robberies.