CHICAGO (CBS) — A recent rash of robberies targeting delivery truck drivers has caught the attention of the U.S. Postal Service.

On Thursday, a robber stole an Amazon delivery truck at gunpoint in the Bridgeport neighborhood, as the driver was returning to the vehicle after dropping off a package.

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No one was hurt, but in the wake of a string of robberies against drivers for UPS, FedEx, and Amazon, as well as U.S. Postal Service mail carriers, the post office is taking additional steps to try to thwart the robbers and keep personnel safe.

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At least seven delivery truck drivers were robbed in Chicago in December, and four more have taken place this week.

The U.S. Postal Inspection Service was reminding mail carriers to be vigilant, and has been coaching them in situations to avoid. In addition, Chicago inspector-in-charge Vic Demtschenko said inspectors and postal police officers are shadowing some mail carriers whose routes already have been targeted.

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Demtschenko said he would love to put a second person aboard every delivery truck, but said that is not feasible for the financially-strapped agency.