Former U.S. Republican presidential candidate Marco Rubio on Sunday ruled out becoming Donald Trump's vice presidential running mate, but said he'd be "honored" to play some kind of a role in helping him win the White House.

Rubio, who clashed bitterly with Trump in the brutal race for the Republican nomination, said his policy differences with the real estate mogul were too great for Rubio to join the ticket.

"I wouldn't be the right choice for him," Rubio said in an extensive interview with CNN's "State of the Union" program. "Donald deserves to have a vice president — he's earned the nomination — and he deserves to have a running mate that more fully embraces some of the things he stands for."