UNITED NATIONS – Israeli Prime Minister Benjamin Netanyahu on Thursday cast the possibility of Iran’s possession of a nuclear weapon as a threat not only to Israel but to the entire world and said the failure to establish “red lines” for Tehran could lead to war.

Netanyahu told the U.N. General Assembly that unless stopped by the international community, Iran could have enough enriched uranium for a nuclear weapon by next summer. He did not threaten to attack Iran, and he said that the United States and Israel are pursuing a united effort to stop the Islamic Republic from developing a weapon.

Near the end of his speech, Netanyahu held up a placard showing a cartoon-like bomb that divided Iran’s efforts into three stages. He said Iran has completed the first stage, developing sufficient low-enriched uranium, and that it is nearing completion of the second stage, the further enrichment of the uranium to weapons grade.

He said that stage could be completed as soon as next summer and that the third stage, preparing an actual weapon, could then be accomplished within “a few months, possibly a few weeks.” He said the effort to build a detonator for the highly enriched uranium would be relatively simple and easily concealed.

Drawing a bright red line across the picture with a marker, he said that Iran must be stopped before it completes the second stage.

“I believe that faced with a clear red line, Iran will back down,” Netanyahu said in the 30-minute address.

Iran’s fast-moving nuclear development program has shadowed the U.N. gathering this year. In his address to the U.N. assembly on Tuesday, President Obama said the United States would do what it must to stop Iran from getting a nuclear bomb.

Obama opposes a unilateral Israeli strike now and says he would authorize a U.S. attack only as a last resort. He insisted Tuesday that there is still time and diplomatic elbow room to negotiate a peaceful end to the most troublesome elements of Iran’s program.

U.S. military and intelligence officials have said that an attack by Israel could ignite chaos and drag the United States into a new Mideast war. They also argue that an Israeli strike would be unlikely to completely destroy the Iranian program, possibly leaving the United States to finish the job.

During the past six months, Netanyahu has made an increasingly public case for a unilateral Israeli attack on Iran sometime soon.

Israel considers Iran its mortal enemy, and Israeli leaders say they cannot afford to risk a nuclear weapon in the hands of a clerical regime pledged to Israel’s destruction.

Netanyahu and his defense minister, Ehud Barak, argue that Iran is moving its sensitive nuclear work deep underground and out of the reach of Israeli conventional bombing capability. Israeli officials privately argue that a quick strike now would damage the program severely and buy more