NEWARK — Three mail carriers on Thursday were robbed at gunpoint by assailants who demanded their mail.

RLS Metro Breaking News reported that one of the carriers was robbed on the 800 block of 16th Street in the city's West Side. Newark police referred questions about the robberies to the U.S. Postal Service police, which on Friday morning did not respond to our request for more information.

Both carriers and outdoor collection boxes have been targeted by thieves around the country.

MassLive.com reports that the Postal Service warned customers to not deposit their mail in a collection box and instead go inside a post office. Theives are taking mail out of the boxes looking for cash and checks that may have been mailed and can be used in identity theft schemes.

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"The biggest variable enticing these criminals to steal are customers depositing mail into blue collection boxes after the last collection of the day or during Sundays and federal holidays," the Postal Service said in a release.

Postal carriers were robbed in Cincinnati for their “arrow key,” a universal key that opens the collection boxes and cluster boxes where mail is stored by carriers awaiting delivery, according to WLWT-TV.

The US Postal Service offers a $50,000 reward for information about robberies of on-duty postal carriers.

The National Association of Letter Carriers also did not respond to our request for more information Friday morning.

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