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.

Israel is widely believed to lack the military capacity to substantially set back Iran’s program without U.S. involvement. 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 that could have devastating consequences, saying there is still time for crippling sanctions to force Iran into a diplomatic settlement.

Netanyahu’s government also is riven by differences over the sanctions and how long it would take Iran to produce a weapon. In the latest evidence of those splits, an Israeli Foreign Ministry report leaked to an Israeli newspaper seemed to suggest Thursday that sanctions could work, saying that the measures have severely cut Iran’s sales of petroleum and access to hard currency to a harsher degree than acknowledged.

Netanyahu pushed back, however, saying that the Iranian economy has been “hit hard” but that sanctions and negotiations between Tehran and the United States, the European Union, China and Russia have failed to halt Iran’s enrichment program.

Speaking with journalists Wednesday, Iranian President Mahmoud Ahmadinejad dismissed the notion that sanctions have seriously hurt his country’s economy and mocked the idea of deeper European sanctions at a time when “the European Union is on the verge of collapse.” He said Iran’s median household income has gone up, the wealth divide has narrowed and oil income has remained steady despite sanctions.

“The overall volume of Iran’s economy has increased incredibly over the past few years,” Ahmadinejad said. “We went from being the world’s 22nd-largest economy to being the world’s 17th-largest economy.”

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.