Two masked robbers armed with what appeared to be a pistol, held up a Moscow post office branch Monday morning and made off with 2.5 million rubles ($83,000), in the second successful robbery of a city post office since Friday, Interfax reported.

Moscow police said Sunday that they had detained a suspect in the holdup of another post office branch late last week in which more than 7 million rubles worth of pension funds was taken, RIA-Novosti reported. Retirees often collect pension payments from their local post office branches.

Police say that robbery appeared to be an inside job, with a contact person at the post office branch tipping off the culprits as to when a large amount of cash would be at the branch.

Police arrested the post office employee and another male suspect on Saturday. At the time of the suspect's arrest, he had 1.3 million rubles with him in a bag. Investigators discovered another 3.7 million rubles and an air gun at the suspect's home.

On Monday, St. Petersburg city police say workers at a post office there foiled an armed robbery, RIA-Novosti reported. The assailants then fled the scene, police said.