A letter carrier was robbed while delivering mail in Alexandria on Wednesday, five days after a post office was held up there, in crimes that officials call unusual anywhere in the United States.

The Wednesday robbery occurred in midafternoon a few blocks from the Braddock Road Metro station in the northwestern part of the city’s Old Town area, authorities said.

The letter carrier was on his rounds in the 700 block of North Fayette Street about 2:45 p.m. when three robbers approached, all wearing masks and one brandishing a gun, U.S. Postal Service spokesman Tom Ouellette said. They took mail and personal property.

On Jan. 10, a man robbed the post office in the 1900 block of Mount Vernon Avenue in the Del Ray section of the city. The incidents are not believed to be connected, Ouellette said.

Post office robberies “are uncommon,” Postal Inspector Frank Schissler said. In a recent 12-month period, postal inspectors investigated a total of 83 robberies of post offices and letter carriers nationwide, he said.

And Ouellette described it as “ extremely unusual” for both a post office and a letter carrier would be robbed in the same city within such a short period.

Two post offices were robbed in the Washington area last year — one on Hamilton Street in Hyattsville and the other in the Seven Corners area of Northern Virginia. An arrest was made in the Hyattsville robbery, authorities said.

A letter carrier was shot and killed last year in Cheverly, but no motive has been disclosed.

All three robbers in Wednesday’s holdup were described as black, slender and in their mid- to late teens. In addition to a mask, each wore blue jeans and a black coat, authorities said.

Two were 5-foot-4 to 5-foot-6 and the third was about two inches taller, they said. People who did not get their mail are encouraged to call postal inspectors at 877-876-2455 (option 2).

The postal service said it is offering a $25,000 reward for information leading to an arrest and conviction in the robbery.