GENEVA - The UN expert on human rights in the occupied Palestinian territories voiced scathing criticism of Israel Monday as he stepped down over what he said was a lack of access to areas he was meant to monitor.

Makarim Wibisono, who took on the role of Special Rapporteur on the rights situation in the Palestinian territories in June 2014, presented his final report to the UN Human Rights Council, criticising Israel's refusal to cooperate with his mandate. "It was with deep regret that I accepted that the premise upon which I took up the mandate... was not fulfilled," he told the council.

The Indonesian diplomat, who had announced in January that he intended to quit, said he had been assured before taking up the position that he would have access to the occupied Palestinian territories. But he said repeated requests for access were unsuccessful.

"This lack of cooperation regrettably seems to signal the continuation of a situation under which Palestinians suffer daily human rights violations under the Israeli occupation," he said, and slammed "a general lack of accountability" for such abuses.

Israel has long accused the Human Rights Council of having a built-in bias against it. It was not present for Wibisono's presentation Monday.

The EU representative, Peter Soerensen of Denmark, said he regretted that Israel had not allowed Wibisono to access the Palestinian territories. But he also noted that his mandate was "limited to investigate Israel's violations", and insisted that all rights abuses, regardless of who committed them, "should be subject to scrutiny."

Palestinian representative Ibrahim Khraishi meanwhile charged that the appointment of Wibisono's successor had been postponed after an Israel-linked rights group had sent out a letter accusing both nominees, British law professor Penny Green and Canadian law professor Michale Lynk, of being anti-Israeli activists.

Khraishi called the delay a "flagrant violation" of the rules of the Human Rights Council. A spokesman for the council meanwhile told AFP there had been "no postponement" of the appointment.

"The process to appoint the (Special Rapporteur) continues and the (council) president continues to consult with a wide range of stakeholders," spokesman Rolando Gomez said in an email, adding that an announcement was expected on Thursday.

In his presentation, Wibisono stressed the need for a successor to continue his work, voicing alarm at the recent escalation of violence committed by both Palestinians and Israelis. According to an AFP count, nearly 200 Palestinians, 28 Israelis, two Americans, an Eritrean and a Sudanese have been killed since October.

While stressing that "any wanton act of individual violence, whether committed by Palestinians or Israelis, is unacceptable and must be investigated and prosecuted," he stressed the violence was happening "in a pre-existing context... against a backdrop of illegal settlements in the West Bank... (and) the blockade of Gaza."

Meanwhile, Hillary Clinton launched a withering attack on Republican frontrunner Donald Trump Monday at an appearance before thousands of Jewish voters, saying America's next president cannot be "neutral" when it comes to Israel.

"We need steady hands, not a president who says he's neutral on Monday, pro-Israel on Tuesday, and who knows what on Wednesday, because everything's negotiable," the Democratic frontrunner told more than 15,000 attendees of American Israel Public Affairs Committee's annual policy conference in Washington. "My friends, Israel's security is non-negotiable."

US presidential hopefuls routinely make pilgrimages to AIPAC during an election year. Republicans Ted Cruz, John Kasich and Trump all are scheduled to address the powerful pro-Israel lobby's confab later Monday.

Trump, who hails from New York, has raised eyebrows in the Jewish community for stressing he wanted to be a neutral broker between Israel and the Palestinians when it came to peace talks.

In a December debate, the billionaire real estate magnate described the Israel-Palestinian relationship as "the toughest negotiation there probably is of any kind."

Clinton stressed the importance of "electing a president with a deep personal commitment to Israel's future."

She also warned against presidential hopefuls who might want to "outsource Middle East security to dictators" or downplay American's national security interests in the region.

"It would be a serious mistake for the United States to abandon our responsibilities or cede the mantle of leadership for global peace and security to anyone else," Clinton said.

Trump, who is the clear frontrunner for the Republican nomination, has insisted he is a steadfast Israel supporter and that no US president would be stronger on US-Israel ties than him. But he has made some Jews and Israel backers bristle, as he did last year when he spoke to the Republican Jewish Coalition.

"I'm a negotiator, like you folks," he told the group, before launching into criticism of President Barack Obama's nuclear deal with Iran, which has been strongly opposed by Israeli Prime Minister Benjamin Netanyahu.

"Is there anybody that doesn't renegotiate deals in this room?" Trump asked. "Perhaps more than any other room I've ever spoken in."

Clinton stressed that Israelis and Palestinians "can't give up" on hopes for peace, but she offered a hard line against perpetrators and supporters of violence recently in the Jewish state.

"These attacks must end immediately," Clinton said. "Palestinian leaders need to stop inciting violence, stop celebrating terrorists as martyrs, and stop paying rewards to their families."

Clinton rival for the Democratic nomination, Senator Bernie Sanders, who is Jewish, declined AIPAC's invitation to address the confab, citing a rigorous campaign schedule in western states.

"Obviously, issues impacting Israel and the Middle East are of the utmost importance to me, to our country and to the world," Sanders said in a letter to AIPAC explaining his absence.

In her comments, Clinton kept alluding to her Republican rivals and particularly Trump, warning against a US foreign policy "that would insult our allies, not engage them, and embolden our adversaries, not defeat them."

"For the security of Israel and the world, we need America to remain a respected global leader... able to block efforts to isolate or attack Israel," she said. "The alternative is unthinkable."

AIPAC has said it was not taking a position on the candidates addressing the conference.