Iran insists that its program is for peaceful purposes. But it has for years refused to answer the U.N. International Atomic Energy Agency’s questions about evidence that it secretly researched a warhead. Tehran also has spurned U.N. demands to halt enrichment, which it has expanded from its main centrifuge plant at Natanz to an airstrike-resistant site beneath a mountain near the holy city of Qom.

The United States and the European Union charge that Iran, which hid its program from U.N. inspectors for 18 years until 2002, is developing the capacity to build a bomb. They have imposed their own sanctions on Tehran, and they’ve been joined by Russia and China in approving four rounds of U.N. measures.

About midway through his speech Thursday, Netanyahu held up the picture of a bomb with a burning fuse – resembling those in children’s cartoons – to illustrate the amount of enriched uranium that Iran has produced, according to the IAEA. In a dramatic fashion, he used a red pen to draw a line at how much more it requires for a weapon.

“Iran is 70 percent of the way there,” he said, referring to the stock of low-enriched uranium that the Islamic republic has refined to almost 20 percent. That level of medium-enriched uranium is more easily and quickly turned into the 90 percent highly enriched uranium required for a warhead.

“Now they’re well into the second stage. And by next spring, at most by next summer at current enrichment rates, they will have finished the medium enrichment and move onto the final stage. From there, it’s only a few months, possibly a few weeks, before they get enough uranium for the first bomb,” he said.

Netanyahu said there would be “little difference” between “a nuclear-armed Iran” and a “nuclear-armed al Qaida,” charging that “they are both fired by the same hatred. They’re both driven by the same lust for violence.”

Several experts said that it appeared that Netanyahu was setting as a red line for a military strike the point at which Iran accumulates enough 20 percent enriched uranium to convert into the amount of highly enriched uranium required for a warhead.

“What he was saying was that once Iran gets what it needs in 20 percent enriched uranium to be able to convert into weapons-grade, that’s when he says Iran should be attacked,” said Greg Theilman, a former State Department intelligence analyst with the Arms Control Association.

Theilman disputed the urgency of Netanyahu’s timeline, saying that Iran’s centrifuge networks would have to be upgraded before they could be used to manufacture highly enriched uranium. IAEA inspectors and monitoring systems inside Iran’s enrichment facilities, he said, would detect the work as soon as it began.

“As soon as they crossed that red line, IAEA inspectors would know about it. The whole international community would know they were racing for a bomb,” he said.

Moreover, Theilman explained, Iran would have to produce more than one device before it represented a credible nuclear threat. The Iran regime couldn’t count on a single device working properly, and it would need more than one to deter Israel, which is widely believed to have several hundred nuclear weapons, or the United States from launching a devastating nuclear counterstrike.

A senior Obama administration official, speaking on condition of anonymity as per diplomatic protocol, said the U.N. Security Council is still pursuing a two-track course of pressure and dialogue. “We all heard the speech today, and we will continue to have our discussions,” the official said of Netanyahu. The official said that while sanctions and pressure are important, diplomacy is the preferred course.

“Iran wants and looks forward to additional dialogue to try to reach an agreement. But that discussion has to be, as I said, a credible one,” the official said. “And we have to make sure that the timetable that’s being used is not just being used to buy time for Iran to continue its nuclear program.”