WASHINGTON • Bolstered by his three caucus victories over the weekend, Senator Bernie Sanders says he wants to debate former secretary of state Hillary Clinton in New York ahead of the Democratic presidential primary election there on April 19, but fears she will not take up the challenge.

His latest remarks reflect his hopes of chipping away at Mrs Clinton's commanding lead in the race to win the party's nomination for the November election, and the belief that he has the political momentum to woo Democratic power brokers to support him.

His advisers consider New York to be a crucial battleground; beating Mrs Clinton in her home state would be a humiliating blow and - perhaps more than any other contest - cast doubts on her strengths as a general election nominee. Yet New York-born Mr Sanders, now a senator for Vermont, would need a big victory in New York to seriously affect her lead.

He told US broadcasters on Sunday that Democratic "super delegates", who can change their allegiance, might face pressure to rally behind him because most polls suggest he has a better chance than Mrs Clinton of beating a Republican rival.

Super delegates - including party leaders and elected senators, members of Congress and governors - hold 15 per cent of the votes and are free to use them as they like at the Democratic National Convention in July, which will choose a candidate for the presidential election. Most are believed to back Mrs Clinton now.

After last Saturday's clear wins for Mr Sanders in Alaska, Washington and Hawaii, Mrs Clinton still leads him by just under 300 delegates in the race for the 2,382 needed to be nominated. But adding the support of super delegates, Mrs Clinton had 1,712 delegates to 1,004 for Mr Sanders, according to a tally by RealClearPolitics.com.

Mr Sanders would need huge wins in future primaries including in California, New Jersey, New York and Pennsylvania to overtake Mrs Clinton, a feat which even some of his staff say is unlikely.

The Washington Post said Mrs Clinton understands the imperative to unite Democrats for the presidential campaign itself and, believing the nomination is nearly locked up, wants to build bridges to Mr Sanders' supporters. An ugly primary in New York threatens to derail those efforts.

Still, Mr Sanders argues that his string of recent wins shows he should not concede the race as a way to unify the party.

"Momentum is with us," he said on CNN's State of the Union programme.

But asked on NBC's Meet the Press if he was worried that Mrs Clinton would not debate him, he replied: "Yeah, I do have a little bit of concern about that."

His campaign manager Jeff Weaver, in a letter to Mrs Clinton's campaign manager, wrote: "Is [Mrs Clinton] concerned about debating before the people who twice elected her to the US Senate?"

A Clinton campaign spokesman declined to comment.

REUTERS, BLOOMBERG, NEW YORK TIMES