SAN DIEGO -- Postal officials say a series of stamp machine burglaries have occurred over the past month at post offices throughout San Diego County, it was reported today.

The bandits last struck Sunday night or early Monday, hitting two locations, one at Second and Peach streets in El Cajon and the other at Austin Drive and Sweetwater Boulevard in Spring Valley, U.S. postal inspector John Lund told The San Diego Union-Tribune.

It was the second time a Spring valley post office was targeted, Lund said. The burglars are also believed to be responsible for thefts in Mira Mesa and Poway.

Lund did not say how the bandits breached the heavy-duty locks, alarm systems and other anti-theft devices built into the machines. He also refused to say how many stamps the machines typically hold, or the amount of money lost, the Union-Tribune reported.

Cameras captured one of the capers and authorities have a witness to one break-in, the newspaper reported. No suspects have been identified.

Postal inspectors are offering up to $10,000 to anyone with information that helps catch and convict those responsible, the Union-Tribune reported.

Anyone with information about the stamp thefts is urged to call (619) 233- 0610.