Two men wearing ski masks and armed with a shotgun are believed responsible for committing six holdups in Northeast Washington over the course of a single week, D.C. police said on Friday.

Several holdups, including on Christmas Eve and Christmas Day, occurred in or near the Brookland neighborhood. Another occurred four miles to the south, between Maryland Avenue and Benning Road Northeast, according to police. The robberies occurred between Dec. 24 and Dec. 31.

Authorities announced a reward up to $10,000 for information leading to an arrest and conviction in the case.

Robberies have been a persistent problem in the District, which saw a spike in January 2012, when the number jumped 61 percent from the previous year.

Police made the issue a priority and the numbers steadily dropped month by month, D.C. Police Chief Cathy L. Lanier said at a news conference on crime this week. By the end of December, Lanier said the spike had all but been erased. The final tally of robberies for 2012 stood at 4,262, six more than occurred in 2011.

The first attack linked to the latest spate of shotgun robberies occurred about 10 p.m. Dec. 24 in the 4000 block of 9th St. NE. Police said two men, one armed with a shotgun, stole a man’s wallet and cellphone.

About 7:15 p.m. on Christmas, police said a man armed with a shotgun forced him into an alley off the 2900 block of 18th St. NE, near Rhode Island Avenue and Langdon Park, and took his cellphone and money.

On Dec. 26 at about 9:55 p.m., police said two man accosted a woman from behind in the 4000 block of 13th St. NE. One announced a robbery and the other threatened the victim with a shotgun, police said. They took the woman’s purse containing a wallet, two cellphones, car keys and driver’s license.

The next holdup occurred Sunday about 2:45 a.m. at 12th Street and Michigan Avenue NE. Police said the men robbed a man of his cellphone and wallet. About 3 1/2 hours later, police said another man was robbed at shotgun-point in the 800 block of 19th Street NE. Police said the men took his cellphone, money, jacket and ID card.

On Monday, police said two people were robbed about 11:35 p.m. at 12th and Randolph streets NE. Police said the assailants came up from behind and announced a robbery. The people “turned around and saw one suspect displaying a shotgun,” police said in a statement. Authorities said purses and cellphones were taken.

Anyone with information about the robberies is urged to call D.C. police at 202-727-9099 or tip the department’s text line at 50411.