Hewlett Packard Enterprise Co chief executive and Republican donor Meg Whitman reiterated her opposition to Donald Trump as the party's presidential nominee and compared him to Adolf Hitler and Benito Mussolini.
Whitman made the comment on Friday (local time) at a conference hosted by previous Republican nominee Mitt Romney, while she challenged US Speaker of the House of Representatives Paul Ryan on his endorsement of Trump, the Washington Post reported on Saturday.
Two participants at the off-the-record session in Park City, Utah confirmed Whitman's language to Reuters. Whitman could not immediately be reached for comment.
A billionaire and former supporter of failed candidate New Jersey Governor Chris Christie, Whitman has been actively working to stop Trump's nomination, including fundraising for an anti-Trump Super PAC.
In February, the technology CEO called Trump "unfit" to be president.
Since then, Trump has become the presumptive Republican nominee and is likely to run against Democratic candidate Hillary Clinton in the November 8 election.
Ryan, addressing the 300 attendees of the session, explained the difficulty he had with the decision to endorse, the Post said, including weathering pressure from House Republicans to lend his backing to Trump.
After weeks of holding out, Ryan endorsed the New York businessman in early June, breaking with a number of establishment Republicans who see Trump's rhetoric as damaging to the party.
The opponents include Romney, Republicans' 2012 presidential nominee, who chose Ryan as his running mate.
Romney has blasted Trump in recent weeks for attacks he has made on the Mexican-American judge presiding over a case against him, with Romney warning on Friday about the effect that "trickle-down racism" could have on the country.