European carrots rather than the American stick appear to have persuaded the Iranian government to suspend a uranium enrichment program that could lead to a nuclear bomb.
And after two years of warning that Europe's negotiations with the clerical regime in Tehran were pointless, Washington seems to be smiling about the deal, even as analysts advise caution about its scope.
Iran announced Sunday that it had reached agreement with Britain, France, and Germany to ease concerns that it was pursuing a nuclear arsenal by indefinitely suspending all uranium enrichment and reprocessing activities that could help make a nuclear bomb.
Though the halt was temporary, Iranian officials said, it would last as long as negotiations with the European Union continue on long-term arrangements to provide "objective guarantees that Iran's nuclear program is exclusively for peaceful purposes," the agreement specified.
In return, the three European governments pledged that the EU would resume talks with Iran about a trade partnership, and support Iran's bid to join the World Trade Organization. (At press time, those governments had not yet confirmed that the deal was signed.)
A similar deal a year ago fell apart after a few months with each side blaming the other for reneging.
That experience feeds suspicions that the new agreement "is a tactical move" by the Iranian government "just to prolong things again" says Ali Ansari, an Iran expert at the Royal Institute for International Affairs, a think tank in London.
Such doubts were widespread in Washington, where the Bush administration has scoffed at the idea of negotiating with a country the president once described as a member of "the axis of evil."
"The Europeans see this as a problem that has to be managed and the US sees it as a threat that has to be confronted now," says Joseph Cirincione, head of the nonproliferation program at the Carnegie Endowment for International Peace in Washington.
Last Friday, however, President Bush appeared to change tack.
At a joint press conference with visiting British Prime Minister Tony Blair, he said "the prime minister gets a lot of credit for working with France and Germany to convince the Iranians to get rid of the processes that would enable them to develop a nuclear weapon."
Outgoing Secretary of State Colin Powell followed that up Sunday by saying bluntly on US television: "We are not getting ready to invade Iran. We have no intention of regime change. That is our policy: no regime change.
Some saw these statements as signs that Washington is backing the European approach. "The US has to get engaged now," says Mr. Cirincione.
"Only the United States can give Iran the security guarantees that it needs to stand down its nuclear weapons program."
Other analysts suggested that Washington was making conciliatory diplomatic noises only because it has no other options at this point.
US Undersecretary of State for Arms Control and International Security John Bolton has long been insisting that the International Atomic Energy Agency board, meeting on Nov. 25, should find Iran in violation of its pledge to disclose all its nuclear activities and refer the issue to the United Nations Security Council.
There, US officials had hoped, they could persuade other members to impose economic sanctions on Iran.
But it has become clear that hardly any other country on the 35-member IAEA board supports the US position, and even if the Iranian problem did come before the Security Council, China would almost certainly veto any sanctions resolution.
At the same time, talk in Washington about the possibility of launching an Iraq-style invasion of Iran has died down.
"The Americans cannot justify doing anything else because now is not the time to deal with Iran," says Mr. Ansari. "They are playing ball with the Europeans to see if it will work one last time.
"But in the grand scheme of things," he adds, "Iran's nuclear program is not the central issue - it is a symptom, not a cause of America's problems with Iran. Their disputes go far deeper, and even if the nuclear question is resolved, that won't stop Iran being the problem for the United States."