STOCKHOLM - The list of troubles linked to Justin Bieber's tour of Europe grew again after Swedish police said Thursday they had found drugs and a stun gun on the pop singer's bus.

No arrests were made since the bus was empty, Stockholm police said.

Police said they decided to act after smelling marijuana coming from inside the bus while it was parked outside the hotel where Bieber was staying in the capital. Drug officers searched the bus during a concert.

A small amount of drugs and a stun gun were discovered during a search of the bus in Stockholm, where Bieber performed Wednesday. Police said the drug was sent to a lab for analysis.

Bieber, who arrived in Helsinki, Finland, Thursday to perform in a concert the following evening, tweeted after his arrival: "some of the rumors about me ... where do people even get this stuff. whatever … back to the music."