A small amount of marijuana was found on Justin Bieber's tour bus before his show in Detroit Sunday night (July 28), a spokesperson for the U.S. Customs and Border Patrol confirmed. The teen heartthrob wasn't on the bus.

Chief officer Kenneth Hammond revealed in an email late Monday (July 29) that agents stopped the vehicle at the Ambassador Bridge as it was crossing into the U.S. from Canada for the remaining stops on Bieber's Believe tour when a search dog alerted agents to the presence of drugs. A personal portion of weed and drug paraphernalia was discovered.

The bus driver was given a citation, and the passengers were released.

Even though he wasn't around for the pot bust, Bieber has admitted to smoking marijuana in the past, admitting it after TMZ posted photos of him with a blunt in hand. The Canadian singer publicly apologized in a Saturday Night Live skit.

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(Photo: Judy Eddy/WENN.com)