Netanyahu has repeatedly argued that time is running out to stop the Islamic Republic from becoming a nuclear power and the threat of force must be seriously considered.
"I believe that faced with a clear red line, Iran will back down — and it will give more time for sanctions and diplomacy," the Israeli prime minister said. "Red lines don't lead to war, red lines prevent war ... nothing could imperil the world more than a nuclear-armed Iran."
Netanyahu's speech marks perhaps his final plea before Israel takes matters into its own hands. Israeli leaders have issued a series of warnings in recent weeks suggesting that if Iran's uranium enrichment program continues it may soon stage a unilateral military strike, flouting even American wishes.
The Obama administration has urgently sought to hold off Israeli military action, which would likely result in the U.S. being pulled into a conflict and cause region-wide mayhem on the eve of American elections.
Israel considers a nuclear-armed Iran to be an existential threat, citing Iranian denials of the Holocaust, its calls for Israel's destruction, its development of missiles capable of striking the Jewish state and its support for hostile Arab militant groups.
"Given this record of Iranian aggression without nuclear weapons, just imagine Iranian aggression with nuclear weapons," Netanyahu said.
Iran insists its nuclear program is for peaceful purposes but Israel, the U.S. and other Western allies reject the claim. Four rounds of U.N. sanctions have already been placed on Iran.
A U.N. report last month only reinforced Israeli fears, finding that Iran has moved more of its uranium enrichment activities into fortified bunkers deep underground where there are impervious to air attack. Enrichment is a key activity in building a bomb, though it has other uses as well, such as producing medical isotopes.
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, even as it develops much of the infrastructure needed to do so.
Obama has repeatedly said he will not allow Iran to gain nuclear weapons and has said the U.S. would be prepared to use force as a last resort.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.
Speaking shortly before Netanyahu, Palestinian President Mahmoud Abbas accused Israel of ethnic cleansing for building settlements in east Jerusalem.
"It is a campaign of ethnic cleansing against the Palestinian people via the demolition of their homes," Abbas said in his speech to the U.N. General Assembly.
Netanyahu rebuked Abbas in his own address, saying: "We won't solve our conflict with libelous speeches at the U.N."
Israel conquered the eastern part of Jerusalem from Jordan during the 1967 Mideast War. It later annexed it but the move has not been internationally recognized. The Palestinians want east Jerusalem to the capital of their future state in the West Bank.
Abbas also said he has opened talks on a new bid for international recognition at the U.N., but didn't specify exactly when he will ask the General Assembly to vote.
"Intensive consultations with the various regional organizations and the state members" were underway, he said.
The Palestinians will apply to the General Assembly for nonmember state status.
That stands in sharp contrast to last year, when they asked the Security Council to admit them as a full member state, but the bid failed.
Abbas insisted that the new quest for recognition was "not seeking to delegitimize Israel, but rather establish a state that should be established: Palestine."
Palestinian officials said their bid is likely to be submitted on Nov. 29.