so. Although Iran continues to enrich uranium at low levels, U.S. officials say they have not seen evidence that has caused them to significantly revise that judgment. Senior U.S. officials say Israel does not dispute the basic intelligence or analysis. But Israel appears to have a lower threshold for action than Washington. It regards Iran as a threat to its existence and says it will not allow Iran to become capable of building and delivering a nuclear weapon. Some Israeli officials have raised the prospect of a military strike to stop Iran before it's too late. It's unclear how much access U.S. intelligence has in Iran, a problem that bedeviled efforts to determine whether Iraq had weapons of mass destruction before the U.S.-led invasion in 2003. The assessment that Saddam Hussein had secretly amassed stockpiles of chemical and biological weapons and was seeking to build a nuclear weapon, cited by the George W. Bush administration to justify the invasion, turned out to be wrong. Iran barred inspectors from the International Atomic Energy Agency , the U.N.'s nuclear watchdog group, from visiting Parchin, a military site, this week to determine whether explosives tests were aimed at developing nuclear technology. An IAEA report in November cited "serious concerns" about "possible military dimensions to Iran's nuclear program," but did not reach hard conclusions. Another IAEA report is imminent. Iran's supreme leader, Ayatollah Ali Khamenei , insisted Wednesday that Tehran had no intention of producing nuclear weapons. In remarks broadcast on state television, he