A woman in her 20s armed with a gun is suspected of robbing four convenience stores or gas stations in Northern Virginia since late December, police said Friday.

The robber first struck on Dec. 29 at a Shell gas station in the Chantilly area, Fairfax County police said, walking in around 10:30 p.m., showing a small silver handgun and demanding cash. The clerk handed over money, and the woman fled in a dark-colored station wagon.

Less than an hour later, police said, a woman with a gun entered a 7-Eleven store in Manassas Park and demanded money. Before the clerk could respond, a customer approached and the woman fled.

Police said a third robbery occurred about 10 p.m. on New Year’s Day at a 7-Eleven store in the Manassas area. After the clerk handed over cash, the woman fled on foot.

The most recent was Jan. 10 at an Exxon gas station in the Falls Church area. In this case, the robber entered the store just after 10 p.m. She wore a black mask over the lower part of her face.

Police said the woman has been described as white, in her early to mid-20s, from 5 foot 3 to 5 foot 7 inches tall. She has worn a dark-colored hooded sweatshirt, jeans or dark-colored pants and has displayed a silver or black handgun. Police said a dark-colored, small station wagon, similar to Subaru Forrester or Outback, has been linked to the woman.

Police in Fairfax and Prince William Counties and Manassas Park are investigating the robberies.