The United States has a mixed record in stopping the spread of nuclear weapons. It did end Taiwan's secret program but let Israel develop atomic bombs. It supports international treaties to keep nations from going nuclear but hasn't done enough under those treaties to reduce its own nuclear arsenal. It invaded Iraq in part to halt any nuclear research but now merely negotiates with a North Korea that's already produced weapons-grade plutonium.
Despite that record, the US now wants Europe, Russia, and Japan to get tougher on Iran for what appear to be that country's lies and deceit in hiding a nuclear weapons effort.
Iran still denies such an effort, but this week the UN's International Atomic Energy Agency (IAEA) said it found traces of highly enriched uranium at Iran's Natanz facilities and hundreds of enrichment centrifuges at a second site, the Kalaye Electric Co. Iran tried to deceive the world by saying that site was a watch factory.
With a Russia-supplied nuclear power plant nearly complete in Iran, the country might be able to produce nuclear weapons within a couple of years. That prospect in a terrorist-supporting nation has Israel, the US, and others demanding action now.
Next month, the IAEA's board could find Iran in violation of the Nuclear Non-Proliferation Treaty and ask the UN Security Council for possible economic sanctions against Iran.
Iran's Islamic leaders are now doing some fast backpedaling on their misdeeds while still denying they want the bomb. Unless they agree, however, to short-notice ("snap") inspections by the IAEA, their credibility will be lost, and sanctions may be the only route.