Sources say there could be “15 to 20 more minutes” of footage yet to be made public in which Justin Bieber makes racial slurs.

Bieber, 20, has battled a scandal over two leaked clips filmed when he was a teen making racist jokes and liberally dropping the N-word.

But a source tells us that further footage “explicitly shows this was more than just one regrettable joke.”

The source added Bieber is shown making cracks about “black people liking watermelon” and asking a friend whether “his parents are as black as [rapper] Akon.”

But a source close to Bieber told us, “This is all the same footage someone had been trying to blackmail Justin over for years. It was made when he was 14 or 15. At the time, he realized it was wrong and went to Usher and Will Smith, who helped educate him. He’s now a 20-year-old who’s taken responsibility.”

Bieber has publicly apologized, and his manager Scooter Braun posted last night, “Some mistakes have no excuses. They are just wrong. But how a man reacts to those mistakes . . . defines him more than the mistake itself.”