A statement from Gallagher on the band's Web site says he's leaving the group "with some sadness and great relief."
The band were due to play a festival in Paris Friday but didn't take the stage. A message flashed to the crowd said "as a result of an altercation within the band, the Oasis gig has been canceled."
Oasis was one of the biggest British bands of the 1990s, with hits like "Wonderwall" and "Champagne Supernova."
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