Justin Bieber smoking a blunt

TMZ has posted some pictures that allegedly show JUSTIN BIEBER smoking pot in a California hotel room.  They were taken last Wednesday.  (You can check them out here.  He's definitely smoking SOMETHING.)

A source says Justin's buddy, 19-year-old rapper LIL TWIST, was there, too.  In fact, it was Twist and his brother who were rolling all the blunts.

Justin hasn't copped to toking, but he did Tweet this after the pictures hit the web . . . quote, "Everyday growing and learning.  Trying to be better.  u get knocked down, u get up.

"Back on tour tomorrow.  Ready to see u all smile.  Time to do what I'm supposed to be doing . . . performing."

In more positive news, Justin visited a 7-year-old leukemia patient Saturday, before a gig in Salt Lake City.

(Gossip Cop, E! Online)