U.S. presidential candidate Hillary Clinton has won surprise backing from the wife of former French President Jacques Chirac, together with a pledge to join her on the campaign trail.

The Chiracs' political affiliations are at the opposite end of the spectrum from the Clintons', but the former French first lady said she had always thought Democratic candidate Clinton had the makings of a U.S. president.

"She's a woman who is not liked by everybody. But she's strong and she has convictions," Bernadette Chirac, well-known for a forceful character of her own, told the weekly Le Figaro magazine.

In the later years of his presidency, Jacques Chirac was widely vilified in the United States for his vocal opposition to the Iraq war led by President George W. Bush. His wife met Clinton several times when her husband Bill Clinton was in the White House before Bush.

"From the first look, the first words, Hillary Clinton is a friendly, smiling person who never lets herself be caught out," she said. She even expressed interest in attending the Democratic convention in Denver in August. "And if I can be of any use to her somewhere in the campaign, I'm available. I'd like to go with her and I'm going to suggest it to her."