| UNITED NATIONS
UNITED NATIONS Israeli Prime Minister Benjamin Netanyahu said on Thursday the world must set a "clear red line" that Tehran must not cross in its nuclear program if Iran is to avoid military action against its atomic facilities.
He appeared to suggest that a decision on whether or not military force could be used against Iran's nuclear facilities may come by the spring of 2013 at the earliest if Iran continues enriching uranium.
Following are questions and answers about Netanyahu's speech to the 193-nation U.N. General Assembly.
WHAT IS THE BACKGROUND?
Israel, the United States, the European Union and their allies say Iran is amassing the capability to produce a nuclear bomb, an allegation the Islamic Republic denies. Tehran is under U.N. and Western sanctions for refusing to halt uranium enrichment, a process that can produce fuel for power plants or bombs.
Netanyahu has presented Iran as a mortal threat to the Jewish state, though not all members of the Israeli government and military share that assessment. Iran says its nuclear ambitions are limited to the peaceful generation of medical isotopes and electricity.
Israel has urged the U.N. Security Council to impose crippling sanctions on Iran, including an oil embargo, but Russia and China, which hold vetoes on the 15-nation body, are opposed to imposing such draconian measures on Iran.
Britain, France, Germany, the United States, Russia and China have been negotiating with Iran without success in one form or another for nearly a decade to persuade it to halt its enrichment program in exchange for political and economic incentives.
Tehran continues to expand its enrichment program and the United States and Israel have both refused to rule out the use of force against Iran's nuclear program. U.S. President Barack Obama told the General Assembly on Tuesday that Washington would do what it takes to prevent Tehran from getting the bomb.
WHAT IS ISRAEL'S "RED LINE"?
Netanyahu said that Iran must not be allowed to amass enough enriched uranium for a single weapon. Using a cartoon-like drawing of a bomb with a fuse, he said Iran's nuclear program had to pass through three stages before it would be capable of producing a bomb.
The first stage is when Iran produces enough low enriched uranium. The second is when it produces enough "medium enriched" uranium. The third and final stage would be when Iran has produced enough "high enriched uranium for the first bomb."
He said the red line must be drawn "before Iran completes the second stage of nuclear enrichment necessary to make a bomb." The timing for that, at Iran's current rate of enrichment, would be by the spring or summer of 2013, he said.
That would suggest that a decision on whether to use military force against Iranian nuclear sites would have to be made by the spring or summer of 2013 as well.
At that point, Netanyahu said, Iran would be a "few months away or a few weeks away from amassing enough enriched uranium to make a nuclear weapon."
HOW MUCH ENRICHED URANIUM DO YOU NEED FOR A BOMB?
According to the U.N. International Atomic Energy Agency (IAEA), a "significant quantity" - enough for a bomb - of uranium enriched to a purity level of 90 percent is 25 kg (55 pounds).
That would mean 25 kg of uranium that is 90 percent uranium-235, which nuclear expert Jeffrey Lewis has described on his blog Arms Control Wonk as "the stuff that goes boom."
Iran has been enriching uranium to 20 percent uranium-235 purity, a level it says is required for medical isotopes but which also is closer to bomb-fuel grade than the uranium Iran used to enrich. According to an August report by the IAEA, Iran has stockpiled 91.4 kg of the 20 percent material.
Some experts say that Iran would need 200 to 250 kg of such material for a weapon, though other experts suggest less might be needed. Iran could potentially reach that threshold soon by producing roughly 15 kg a month, a rate that could be speeded up if it activates new enrichment centrifuges.
Netanyahu was not entirely clear on this point, but he appeared to suggest that if Iran were to acquire enough 20 percent enriched uranium needed for a single bomb, it would have crossed his proposed "red line" and could face military action.
Even if Iran acquired 200-250 kg of 20 percent enriched uranium, it would still need to enrich it to bomb grade level of 90 percent or higher to make it usable in a weapon.
HAS ISRAEL ATTACKED NUCLEAR SITES BEFORE?
Yes, twice. In 1981, Israel launched air strikes against Iraq's Osirak nuclear reactor that was under construction near Baghdad after the Israelis determined that the Iraqis were getting ready to load nuclear fuel into it. The raid destroyed the reactor.
In 2007, Israel attacked a site in Syria that Israeli officials said was a nuclear plant under construction with North Korean assistance. They said the plant was demolished.
Attacking Iran's nuclear program, diplomats and analysts say, would be much more challenging than Iraq's or Syria's because Iranian facilities are spread around dozens of sites across Iran's vast territory, some of them underground.
Netanyahu said Iran's uranium plants were visible and vulnerable. "These enrichment facilities are the only nuclear installations that we can definitely see and credibly target," he said.
(Reporting By Louis Charbonneau; Editing by Claudia Parsons)