The influential group, which pushes for tax cuts and less government regulation, has made clear that beating former president Trump in the primaries is a top priority, as they think he would lose the November 2024 election to President Joe Biden. Biden beat incumbent Trump in the 2020 White House race.

"We would support a candidate capable of turning the page on Washington's toxic culture - and a candidate who can win. And last night, we concluded that analysis," the Koch group, Americans for Prosperity Action, said in a statement.

"That candidate is Nikki Haley."

The group said its internal polling confirms anecdotal reports from activists on the ground on what they are hearing from voters in states with early presidential nominating contests.

They show Haley, the former ambassador to the United Nations, is in the best position to defeat Trump in the Republican primary, it said. Internal polling also "consistently shows" that Haley is the strongest candidate by far to beat Biden in a general election, it said.

Public opinion polls show Haley battling with Florida Governor Ron DeSantis for a distant second place behind Trump.

The super-PAC has raised over $70 million to spend on political races, an official with the group said in July.

"In sharp contrast to recent elections that were dominated by the negative baggage of Donald Trump and in which good candidates lost races that should have been won, Nikki Haley, at the top of the ticket, would boost candidates up and down the ballot, winning the key independent and moderate voters that Trump has no chance to win," it said.

The group promised Haley "the full weight and scope of AFP Action's unmatched grassroots army and resources" in her bid to become the next U.S. president.

(Reporting by Doina Chiacu; Editing by Alistair Bell)

By Doina Chiacu