"At this late hour, there is only one way to peacefully prevent Iran from getting atomic bombs," Netanyahu said. "And that's by placing a clear red line on Iran's nuclear weapons program," a line that triggers military action.
Speaking to the U.N. General Assembly, Netanyahu argued, "Red lines don't lead to war. Red lines prevent war," citing a number of historical examples.
"Clear red lines have also worked with Iran," he said. "Earlier this year, Iran threatened to close the Straits of Hormuz. The United States drew a clear red line, and Iran backed off.
"Now, red lines could be drawn in different parts of Iran's nuclear weapons program," he added. "But to be credible, a red line must be drawn, first and foremost in one vital part of their program, on Iran's efforts to enrich uranium."
He contended Iran could produce medium enriched uranium by next spring, and weapons grade product shortly thereafter.
If Iran gets the atomic bomb, he asked, "Who among you would feel safe in the Middle East? Who'd be safe in Europe? Who'd be safe in America? Who'd be safe anywhere?"
Netanyahu argued sanctions against Iran will not work.
"For over seven years ... the international community has tried sanctions with Iran," he said. "Under the leadership of (U.S.) President Obama, the international community has passed some of the strongest sanctions to date. ... It's had an effect. Oil exports have been curbed, and the Iranian economy has been hit hard. It's had an effect on the economy, but we must face the truth, sanctions have not stopped Iran's nuclear program either."
Earlier at the United Nations, Palestinian President Mahmoud Abbas said Israel rejects the "two-state solution" for peace.
"President Abbas just spoke here," Netanyahu said. "I say to him and I say to you, we won't solve our conflict with libelous speeches at the U.N. ... We won't solve our conflict with unilateral declarations of statehood."