MILWAUKEE (REUTERS) - United States President Donald Trump threw his support, welcome or not, behind Democratic presidential contender Bernie Sanders in his back-and-forth with rival Elizabeth Warren, saying he did not believe Mr Sanders would suggest a woman could not win the 2020 election.

Tensions between Ms Warren and Mr Sanders, two progressive US senators who are running for the Democratic nomination, have risen after a report that Mr Sanders told Ms Warren in 2018 that he did not believe a woman could beat Mr Trump.

Ms Warren confirmed the report late on Monday in a statement, saying: "I thought a woman could win; he disagreed."

Mr Sanders has denied making such a statement.

Mr Trump, at a rally in Wisconsin on Tuesday, sided with the self-described democratic socialist.

"I don't believe that Bernie said that. I really don't. It's not the kind of a thing he would say," Mr Trump said, adding that he did not know Mr Sanders and did not like him.

Mr Trump beat former Secretary of State Hillary Clinton in the 2016 White House race.