During the UN General Assembly , Netanyahu drew a red line across a cartoon bomb to illustrate the point at which he said Iran will have amassed enough uranium at 20 percent fissile purity to fuel one nuclear bomb if enriched further. He said then that Iran could reach that threshold by mid-2013.
Last week, Amos Yadlin, a former chief of Israel's Military Intelligence, warned that the Iranians would hit a breakthrough with its atomic program by summer, setting the two countries on a collision course.
Netanyahu said at a meeting on Monday of his Likud-Beiteinu Knesset faction that Iran's nuclear activities remained short of his benchmark.
"Iran is continuing with its nuclear program. It has yet to cross the red line I presented at the United Nations, but it is approaching it systematically," he said in broadcast remarks. "It must not be allowed to cross it."
The Islamic Republic says it is enriching uranium only for peaceful energy and medical purposes.
Israel, widely believed to be the Middle East's only nuclear-armed power, has issued veiled warnings for years that it might attack Iran if international sanctions and big power diplomacy fail to curb what it regards as a drive by Tehran to develop atomic weapons.
Israel has long insisted on the need for a convincing military threat and setting clear lines beyond which Iran's nuclear activity should not advance. It says this is the only way to persuade Iran to bow to international pressure by curbing enrichment activity and allowing unfettered UN inspections.
During Monday's meeting, Netanyahu also addressed other threats faced by Israel, including the civil war in Syria and rocket fire from the Gaza Strip.
"Syria is falling apart," he said. "New forces are taking hold of the country, posing two possible risks: a strike on the Golan Heights and lethal weapons falling into the hands of Hezbollah and other terror groups.
"We're monitoring all these developments … we won't allow our citizens to be hurt, neither in the south nor in the north. We won't allow the strikes from Gaza to continue. We will respond with much mightier force."
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