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Dana White says he's not sure if Nate Diaz or his brother Nick Diaz will ever fight in the UFC again -- telling TMZ Sports straight-up, "They don't seem like they wanna fight."

Dana says the UFC has offered multiple fights to both Diaz brothers but they keep turning them down -- and White says he's not really sure why.

"If they want to fight next week or if they never want to fight again, that's up to them. It's not up to me," White says.

"They don't seem like they wanna fight ... either one of them."

White also responded to incendiary comments Nate made on "The MMA Hour" on Wednesday about his rematch with Conor McGregor ... a fight Nate lost by decision.

"The decision went to him because the company wanted it to go to him," Nate said (around 15:30 in the YouTube clip).