Sliding a red marker across the diagram of a bomb while standing at the podium at the United Nations General Assembly, he said it should be stopped before the nuclear program -- which Iran says is for energy but which Netanyahu claims is a proxy for a nuclear weapon -- is 90 percent complete.
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"The red line should be drawn right here, before Iran completes the second stage of nuclear enrichment necessary to make a bomb," he said, adding, "before Iran gets to a point where it's a few months away or a few weeks away from amassing enough enriched uranium to make a nuclear weapon."
In a half-hour speech, Netanyahu all but dismissed the charge by Palestinian Authority President Mahmoud Abbas that Israel has shown over the past year that it "rejects the two-state solution" to the Israeli-Palestinian conflict. Abbas said he would seek nonmember status in the General Assembly this year.
Netanyahu called Abbas' charges "libelous" and reiterated a point he made last year that the conflicts between Israel and the Palestinians will not be solved through speeches at the UN.
But he reserved the bulk of his half-hour speech to make the case for dealing with an Iran he believes is working to build a nuclear weapon, which he said International Atomic Energy Agency reports reveal is 70 percent complete.
"The relevant question is not when Iran will get the bomb," Netanyahu said. "The relevant question is what stage can we no longer stop Iran from getting the bomb? . . . I believe that, faced with a clear red line, Iran will back down and this will give more time for sanctions and diplomacy to convince Iran to dismantle its enrichment program altogether."
He made the case that Iran is a danger to the world by comparing it to al-Qaida.
"To understand what the world would be like with a nuclear-armed Iran, just imagine what the world would be like with a nuclear-armed al-Qaida," he said.
"It makes little difference whether these lethal weapons are in the hands of the world's most dangerous terrorist regime or the world's most dangerous terrorist organization. They are both fired by the same hatred. They are both driven by the same lust for violence."
Abbas began his talk reporting that Israelis in "terrorist militias" have engaged in "relentless waves of attacks" on Palestinians in the occupied territories despite ongoing talks. He said there were 535 attacks in the past 12 months.
A tolerance for those attacks and continued building of Israeli settlements, coupled with what he said was a lack of fruitful talks, led him to the conclusion that Israel is not serious about creating a two-state solution.
"The escalation of settler attacks should not surprise anyone, for it is the inherent byproduct of the continuation of occupation and a government policy that deliberately fosters the settlements and settlers, and deems their satisfaction to be an absolute priority," he said.
Abbas noted that his attempt to create statehood by applying for membership in the United Nations through the Security Council last year was "aborted" and said his new approach of seeking nonmember status through the General Assembly is an intermediate step toward creating an independent Palestinian state.