Secretary of State Condoleezza Rice on Tuesday warned the United Nations' chief nuclear inspector not to complicate the international ultimatum to Iran to shutter disputed atomic work, saying diplomacy is best left to diplomats.

"It is not up to anybody to diminish or to begin to cut back on the obligations that the Iranians have been ordered to take" by the U.N. Security Council, Rice said.

Although she did not mention U.N. nuclear watchdog Mohamed ElBaradei by name, Rice was referring to his plan, widely seen as an attempt to head off a third round of U.N. sanctions, to account for Iran's past nuclear behavior.

ElBaradei said Monday that nations critical of his last-ditch effort should wait until the end of the year to see whether Iran answers outstanding questions before taking any other action.

Rice said Iran may not be sincere in its agreement with ElBaradei's International Atomic Energy Agency to resolve technical questions about the origin, scope and purpose of its once-secret nuclear research. Iran claims the program is peaceful, but the United States and other nations suspect that Tehran is working to build a bomb.

"The IAEA is not in the business of diplomacy," Rice said with undisguised irritation. "The IAEA is a technical agency" whose role is to inspect nuclear facilities and report on and enforce nuclear agreements, she said.

In blunt language unusual among diplomats, Rice suggested that the IAEA's board and director are freelancing where they do not belong.

"There are a lot of elements that the IAEA needs to be concerned with, and the one that they need to be concerned with Iran is ... whether and when and if they are living up to the agreements that they have signed," Rice told reporters traveling with her to the Mideast.

ElBaradei also said Iran's harshest critics should learn from the Iraq invasion and refrain from "hype" about a possible military attack, calling force an option of last resort.

The Nobel laureate is an old Rice nemesis. They have differed publicly for years, including over the run-up to the U.S.-led invasion of Iraq in 2003, when Rice was President Bush's national security adviser.

On Tuesday, Rice called the recent IAEA agreement with Iran over outstanding nuclear questions "a good thing." In the next breath she added: "But this wouldn't be the first time that the Iranians made an agreement only to break it."

Rice said the United States and its partners will move forward with a request for a third round of Security Council sanctions. She said she will discuss sanctions this month with other members of the six-nation international bloc that has offered Iran economic incentives if it gives up uranium enrichment and other activities that worry the West.

The Security Council is not expected to take up the issue before October. Iran has ignored the previous U.N. demands and associated mild sanctions. It is not clear whether the United States can win a third round.

"We believe the diplomatic track can work, but it has to work both with a set of incentives and a set of teeth," Rice said.

The Bush administration has pursued a cautious outreach to Iran despite internal divisions over how best to contain or counter Iran's growing regional ambitions and alleged nuclear weapons program.

Rice declined comment on remarks over the weekend from her French counterpart warning of possible war with Iran.

French Foreign Minister Bernard Kouchner on Sunday said "we must prepare ourselves for the worst" if Iran obtains nuclear weapons, and he specified that could mean a war.

He appeared to soften the warning a bit on Tuesday, emphasizing instead a need to "negotiate, negotiate, negotiate without respite."

Kouchner is meeting Rice in Washington on Friday.