A White House official derisively dismissed John McCain's opposition to Donald Trump's CIA nominee in a closed-door staff meeting, saying the senator from Arizona battling brain cancer is “dying anyway”, according to another White House official with knowledge of the comment.

Kelly Sadler, a special assistant in the communications office who helps manage talking points for Trump allies, reportedly made the comment about McCain during a discussion among the White House communications staffers about Gina Haspel's nomination for CIA director, which the Arizona Republican announced Wednesday that he opposed.

“It doesn't matter, he's dying anyway,” Ms Sadler said, according to the official with knowledge of the comment, who spoke on the condition of anonymity because remarks made during internal meetings are intended to remain confidential. Her comment was first reported by The Hill and confirmed by The Washington Post.

A White House spokesman did not dispute the report and issued a statement on behalf of the White House: “We respect Senator McCain's service to our nation and he and his family are in our prayers during this difficult time.” Ms Haspel, the CIA's acting director, issued a statement: “I have the utmost respect for Senator McCain and I appreciate the thoughtfulness with which he has approached this nomination process.”

The senator's wife, Cindy McCain, said in a Twitter message targeted at Ms Sadler on Thursday evening: “May I remind you my husband has a family, 7 children and 5 grandchildren.”

Ms Sadler's comment comes amid tension between the White House and Mr McCain, 81, who has been at home in Arizona fighting brain cancer. Mr McCain - a Navy officer who was captured in Vietnam after his aircraft crashed and was tortured as a prisoner of war - urged his Senate colleagues to oppose Ms Haspel's nomination.

After watching Ms Haspel's Senate testimony Wednesday, Mr McCain issued a statement saying that although Ms Haspel is “a patriot” and a longtime public servant, her past work at the CIA overseeing interrogation programmes was “disturbing".

“Her refusal to acknowledge torture's immorality is disqualifying,” Mr McCain wrote in a statement. “I believe the Senate should exercise its duty of advice and consent and reject this nomination.”

The fraught relationship between Mr McCain and Mr Trump dates back several years. In the summer of 2015, shortly after launching his presidential campaign, Mr Trump mocked Mr McCain's war service, saying of the 2008 Republican presidential nominee: “He's not a war hero. He's a war hero because he was captured. I like people that weren't captured.”