Prime Minister Benjamin Netanyahu left for New York in the immediate aftermath of the Yom Kippur fast on Wednesday evening, to address the annual General Assembly of the United Nations on Thursday and conduct meetings with several world leaders.

Shortly before flying out, Netanyahu bitterly castigated Iranian President Mahmoud Ahmadinejad’s speech to the UN earlier Wednesday, and those who stayed in the room to hear it. “On the day that we pray to be inscribed in the Book of Life,” the prime minister said in reference to Yom Kippur, “the authoritarian Iranian regime takes every opportunity to condemn us to death.”

He added: “The Iranian oppressor chose to call in public, in front of the entire world, for our disappearance… That is a black day for those who chose to to remain in the room and listen to these accusatory words.”

Netanyahu said his own speech on Thursday would constitute “our response,” and also pledged to “use every possible means” to prevent Iran from acquiring a nuclear weapon. History had proven, he said, that those who sought to destroy the Jews failed in the attempt.

Netanyahu’s speech, which aides said would contain “significant” content, might be tweaked until the last minute, officials told The Times of Israel. Netanyahu will be speaking shortly after Palestinian Authority President Mahmoud Abbas addresses the gathering.

A report Tuesday in Maariv claimed Netanyahu would specify “red lines” which, if crossed by Iran, would prompt military action. But officials did not confirm this, although it is understood that the address will focus primarily on the Iranian threat, and go into detail about Tehran’s nuclear program and the specifics of the advances made by Iran despite international sanctions.

“I will reiterate that the most dangerous country in the world must not be allowed to arm itself with the most dangerous weapon in the world,” Netanyahu said Sunday during the weekly cabinet meeting.

Netanyahu is expected to try to rally support for tougher sanctions and underline his demand that the international community — most especially the United States — halt Iran’s race to a nuclear weapons capability.

In announcing four weeks ago that he had decided to fly to New York for the gathering — even though it falls inconveniently in the Jewish calendar, beginning on Yom Kippur and ending just ahead of Sukkot — Netanyahu said he was going “to tell the nations of the world in a loud and clear voice the truth about the Iranian regime of terror, which constitutes the greatest threat to world peace.”

Surprisingly, Netanyahu’s visit will not include a meeting with Obama, because of what the White House claimed were scheduling difficulties. At one point the White House said no such meeting had been sought, prompting the remarkable charge by an unnamed aide to the prime minister that the White House was lying.

Although Obama, in the midst of his reelection campaign, with elections just weeks away, has not been meeting with any foreign leaders during his time in New York, his unwillingness to make time for Netanyahu has been widely discussed in American media. Some newspapers pointed out that he did find room in his schedule for appearances on several talk shows in recent days, including an interview with ABC’s “The View” on Monday.

The failure to overcome the scheduling difficulties appears to underline the tensions and differences between the two allied leaderships on Iran — not as regards the threat posed by the rogue nuclear program, but as regards the urgency of a possible resort to military force.

Netanyahu had indicated in recent months that he was contemplating ordering a military strike at Iranian nuclear facilities, but the administration made public its opposition to the idea. Appearing to backtrack, the prime minister urged Obama to at least publicly set “red lines” for US-led military intervention, but was rebuffed again.

A bitter Netanyahu then declared that those who were not prepared to set red lines for Iran had no “moral right to place a red light” in front of a possible Israeli strike.

Obama, in a TV interview earlier this week, appeared to dismiss the pressure from Netanyahu for a tougher stance on Iran as “noise,” and his staff proved immovable as regards a possible meeting, even though the prime minister’s aides indicated that he would fly from New York to Washington if necessary.

Is Mahmoud Abbas willing to resume talks with Israel?

Netanyahu’s delegation will arrive in New York on Thursday morning, just a few hours before his scheduled speech.

Addressing the gathering an hour ahead of him, Abbas is expected to announce his intention in principle to ask the General Assembly to upgrade Palestine’s status from that of an observer entity to a non-member state — a move opposed by Israel and the US, but one that is much less dramatic than his failed bid last September to have Palestine admitted by the UN Security Council as a full-fledged UN member state.

Jerusalem is staunchly opposed to the Palestinian gambit, with officials insisting that a genuine resolution of the conflict can only result from negotiations between the two sides and not unilateral actions. Israeli leaders know that the 193 member-states of the General Assembly, where no country has a veto right, would overwhelmingly vote in favor of upgrading Palestine.

Abbas has reportedly promised Obama to hold off on formally seeking the upgrade at this week’s GA, and to do so, instead, only after the US presidential elections in November.

On Tuesday, Haaretz reported that Abbas has agreed to resume negotiations with Israel if Jerusalem freezes all settlement construction in the West Bank. Abbas also promised “a positive statement” about the historic connection between Israel and the Jewish people during his address, according to the paper.

Netanyahu, who is being accompanied to New York by his wife Sarah, is staying in the US for only three days. On Thursday, after his speech, he will meet with European Union foreign policy chief Catherine Ashton, UN Secretary-General Ban Ki-Moon and US Secretary of State Hilary Clinton.

Minutes after the Sabbath ends, the prime minister’s delegation will head back to the airport to arrive in Israel on Sunday afternoon, hours before the start of the Sukkot holiday.