As Washington presses its drive to thwart Iran's suspected efforts to build a nuclear bomb, it is turning increasingly to the same diplomatic rhetoric used in the runup to the Iraq war.

Nobody here is talking seriously about a full-scale invasion of Iran like the 2003 move to oust Saddam Hussein for allegedly developing weapons of mass destruction that were never found.

When asked about the possibility, Secretary of State Condoleezza Rice has a stock answer: "Iran is not Iraq. I know that's what's on people's minds. The circumstances are different."

Nevertheless, US officials appear in much the same position as they were in 2002: stalwart defenders of the nuclear order scouting world support for their cause, uncompromising souls in a compromising multilateralist universe.

With the latest nuclear crisis coming to a head after Iran blew off a UN Security Council injunction to halt uranium enrichment, the United States is again showing signs of frustration with the world body.

Nearly four years after President George W. Bush warned the United Nations it risked becoming "irrelevant" unless it dealt with Saddam, his administration is billing the showdown with Iran as a new test of UN mettle.

"Iran is openly challenging the United Nations," deputy State Department spokesman Adam Ereli said Friday. "That challenge should have consequences in order to sustain and to reinforce the credibility of the UN as an institution."

Faced with stubborn resistance from veto-wielding Security Council members Russia and China to punitive measures against Iran, Washington is working on an alternative to UN action as it did for Iraq.