While Israel is convinced that Iran is pursuing a nuclear weapon, American officials believe Iran has not yet made a final decision to take the plunge and that there is still time for diplomacy.
Iran's talks with world powers over the issue have stalled, however, and Netanyahu argued Thursday that "Iran uses diplomatic negotiations as a means to buy time to advance its nuclear program.''
Israel's timeline for military action is shorter than that of the United States, which has far more powerful bunker-busting bombs at its disposal, and there is great suspicion in Israel over whether in the moment of truth Obama will follow through on his pledge.
"Each day, that point is getting closer. That's why I speak today with such a sense of urgency. And that's why everyone should have a sense of urgency,'' Netanyahu said. "The relevant question is not when Iran will get the bomb. The relevant question is at what stage can we no longer stop Iran from getting the bomb.''
Netanyahu has a history of fiery speeches about Iran before the U.N. General Assembly.
In 2009, he waved the blueprints for the Nazi death camp Auschwitz and invoked the memory of his own family members murdered by the Nazis while making his case against Iran's Holocaust denial and threats to destroy Israel. And last year, he warned about "the specter of nuclear terrorism'' if Iran were not stopped.
While the bulk of Netanyahu's speech dealt with Iran, he also rebuked Palestinian President Mahmoud Abbas, who spoke shortly before him to the U.N. General Assembly and accused Israel of ethnic cleansing for building settlements in east Jerusalem.
"We won't solve our conflict with libelous speeches at the U.N.,'' Netanyahu said. "We have to sit together, negotiate together and reach a mutual compromise.''
Israel captured the eastern part of Jerusalem from Jordan during the 1967 Mideast War and later annexed it in a move that hasn't been recognized internationally. The Palestinians claim east Jerusalem as the capital of their future state along with the Gaza Strip and the rest of the West Bank.
In his speech, Abbas also said he had opened talks on a new bid for international recognition at the U.N.
The Palestinians will apply to the General Assembly for nonmember state status, in stark contrast to last year's failed bid to have the Security Council admit them as a full member state.
If Palestine does become a U.N. observer state, it will not have voting rights in the world body but will have international recognition as a "state.'' This could enhance the possibility of the Palestinians joining U.N. agencies and becoming parties to treaties including the International Court of Justice or the International Criminal Court.
Abbas insisted that the new quest for recognition was "not seeking to delegitimize Israel, but rather establish a state that should be established: Palestine.''