U.S. border agents say they found marijuana on a bus with Canadian pop star Justin Bieber's tour as it crossed into Detroit from Windsor, Ont.

U.S. Customs and Border Protection spokesman Ken Hammond told the Detroit Free Press that the bus was stopped Sunday as it attempted to enter the U.S. on the Ambassador Bridge, The Associated Press reports.

The singer was not on the bus at the time and performed later that night at Joe Louis Arena as part of his Believe tour.

Hammond says a police dog indicated the presence of drugs on the bus and that drug paraphernalia and a small amount of marijuana were found.

He said the bus driver was cited, and that the bus and its passengers were allowed to go.

Bieber is on a North American tour that has included stops in Toronto, where he had back-to-back concerts at the Air Canada Centre.

The incident at the Detroit-U.S. border follows a series of headline-making antics by the Stratford, Ont.-raised teen singer.

They include running into problems dealing with:

With files from CBC News