An Israeli envoy on Sunday assailed leading US presidential hopeful Bernie Sanders as a "fool" as the conference of the pro-Israel lobby laid bare divisions over right-wing Prime Minister Benjamin Netanyahu.

Sanders is staying away from the annual conference of AIPAC, saying it offers a platform for "leaders who express bigotry and oppose basic Palestinian rights," and has denounced Netanyahu as a "reactionary racist."

Israeli Ambassador to the United Nations Danny Danon, a member of Netanyahu's Likud Party, wasted no time in denouncing Sanders as thousands of AIPAC activists opened their meeting at a Washington conference center.

"We don't want Sanders at AIPAC. We don't want him in Israel," Danon said.

"Anyone who calls our prime minister a 'racist' is either a liar, an ignorant fool, or both," Danon said.

Sanders, who would be the first Jewish US president, lived on a kibbutz in Israel in the 1960s and calls himself a supporter of the country but has voiced alarm at its rightward turn under Netanyahu.

Netanyahu has vowed to annex much of the occupied West Bank if he secures another term in elections Monday -- the third time Israelis are voting in less than a year amid a political deadlock.

Democratic White House hopeful Bernie Sanders speaks during a campaign rally at the Virginia Wesleyan University
Democratic White House hopeful Bernie Sanders speaks during a campaign rally at the Virginia Wesleyan University AFP / Eric BARADAT

Ex-military chief Benny Gantz, Netanyahu's centrist rival, addressed AIPAC via satellite and, without mentioning Sanders, vowed to rebuild support for Israel in the United States.

"I will instill hope and not hate. That is the Israel we know; that is the Israel we need," Gantz said to applause.

"Israel will never, ever become a partisan issue," he said. "I will work effectively across both sides of the aisle."

Gantz presented few differences with Netanyahu on security policy and praised a controversial Middle East plan recently proposed by President Donald Trump, which would allow a restricted Palestinian state.

But Gantz said he would oppose far-right politicians seeking to enter parliament and, in an issue important to many American Jews, promised to ensure inclusion at the Western Wall, Judaism's holiest site where women are restricted.

Howard Kohr, the head of AIPAC, which stands for the American Israel Public Affairs Committee, warned of dire risks for the lobby's agenda in November elections, without naming Sanders.

"A growing and highly vocal and energized part of the electorate fundamentally rejects the value of the US-Israel alliance," Kohr said, saying the alliance's foundation "is in danger of being rocked as it has never been before."