UNITED NATIONS – Armed with a cartoon-like picture of a smoldering bomb, Israeli Prime Minister Benjamin Netanyahu called Thursday on the world to set a "clear red line" on Iran's enrichment of uranium, warning that Iran must be stopped before it accumulates enough material to produce warhead fuel.

Netanyahu told the U.N. General Assembly that Iran could manufacture a sufficient stock of enriched uranium for a weapon by next summer. While he didn't explicitly restate earlier threats to strike Iran's nuclear facilities to prevent it from doing so, his meaning was clear.

"The red line must be drawn on Iran's nuclear enrichment program because these enrichment facilities are the only nuclear installations that we can see and credibly target," he said. "I believe that faced with a clear red line, Iran will back down, and it will give more time for sanctions and diplomacy.

"Nothing could imperil the world more than a nuclear-armed Iran," said Netanyahu, who views Iran as an existential threat to Israel, citing Iranian leaders' denial of the Holocaust, arsenal of ballistic missiles and statements that the Jewish state shouldn't exist. He also warned U.N. delegates that Iran could slip a nuclear weapon to Islamic terrorists.

President Barack Obama, speaking to the General Assembly on Tuesday, said the United States would "do what it must" to prevent Iran from developing a warhead. But he has rejected calls that he set an ultimatum for military action, saying there is time for sanctions to force Iran into a diplomatic settlement.

Enrichment involves thousands of interconnected, high-speed centrifuges refining uranium hexafluoride gas into low-enriched uranium for power reactors and medical isotopes and highly enriched uranium for bomb fuel, depending on the duration of the refining process.

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.

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.

During 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.

Greg Theilman, a former State Department intelligence analyst, disputed the urgency of Netanyahu's timeline, saying Iran's centrifuge networks would have to be upgraded before they could be used to manufacture highly enriched uranium.

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