The United Nations nuclear watchdog's vote to rebuke Iran on Friday should send a clear message that Tehran will face consequences if it fails to engage with major powers on the nuclear issue, a senior U.S. official said.

"We hope that the board of governors resolution reinforces the message that, you know, we're committed to putting together a package of consequences if we don't find a willing partner. We hope Iran takes note of that clear message," the official told reporters on condition of anonymity.

The International Atomic Energy Agency's board of governors voted 25-3 to censure Iran for developing a uranium enrichment site in secret in a motion that gained rare backing from Russia and China, which have in the past blocked attempts to isolate Iran, a trade partner for both.

The U.S. envoy to the IAEA, Ambassador Glynn Davies, said in Vienna on Friday that international patience with Iran was running out and that "round after round" of fruitless talks could not continue.

Speaking to reporters in Washington later, the U.S. official said the vote showed "unity of purpose" among major international powers on Iran, and repeated that time was growing short for Tehran to come clean about a nuclear program that Western governments fear is aimed at producing nuclear weapons. Iran denies the charge.

The official declined to be drawn on what sort of consequences were being contemplated, although British Prime Minister Gordon Brown said harsher sanctions could be on the way if Iran ignored the IAEA vote.

U.S. President Barack Obama and European leaders have given Iran until the end of the year to begin talks on the nuclear stalemate.

The U.S. official said Russia and China, along with other negotiators United States, Britain, France, and Germany, were agreed on what should happen next if Tehran fails to respond.

"It is significant, as I said before, that both of those parties strongly supported this step in the board of governors," the official said, referring to Russia and China.

"They are fully committed to a two-track strategy ... we intend to take this very steadily and step by step."

Another U.S. official said China - seen as the most reluctant of the five permanent members of the UN Security Council to sanction Iran - had played a useful role in the IAEA discussion and even suggested language that was included in the final resolution.

"They had a certain degree of authorship," the official, also speaking on condition of anonymity, said, calling final passage of the resolution "very much a collective effort."

The resolution was the first by the 35-nation governing board in almost four years. With rare Russian and Chinese backing, it sent a message of international exasperation with Iran's nuclear secrecy and defiance.

Most developing nations on the IAEA board, who are in a bloc that includes Iran, opposed the move, saying it would be provocative and counterproductive. Iran warned it would undermine its relations with the IAEA.

But supporters were provoked by the September revelation of a second enrichment site Iran had been building for at least two years, a subterfuge they said fanned suspicions of more secret sites that could be dedicated to making atom bombs.

The measure also signaled diminishing tolerance of Iran's reluctance to embrace an IAEA-brokered plan to provide it with fuel for a nuclear medicine reactor if it gives up enriched uranium that could be turned into bomb material if further refined.

The draft resolution urged Iran to immediately halt construction of the Fordow enrichment plant, located in a mountain bunker, and to clarify its original purpose and confirm it has no more hidden atomic facilities or clandestine plans for any. Iran denies it wants to build nuclear weapons, saying its atomic energy program is purely for peaceful purposes.

Iran's envoy to the IAEA, Ali Asghar Soltanieh, called the resolution a "hasty and undue" step.

"Adoption of this resolution is not only unhelpful in improving the current situation, but it will jeopardize the conducive environment vitally needed for success in the process of Geneva and Vienna negotiations expected to lead to a common understanding," he said.

Developing nations argued in pre-vote debate that the resolution would be provocative and counterproductive.

But supporters were provoked by the September revelation of a second enrichment site that Iran had been building for at least two years, a subterfuge they said fanned suspicions of more secret sites that could be dedicated to making atom bombs.

Earlier Friday, Iran warned the IAEA not to use threatening language against Tehran.

"We recommend the IAEA not to refer to such methods and use the language of logic rather than force," the official IRNA news agency quoted Soltanieh as saying.

The Iranian envoy added that a draft resolution tabled at the IAEA's Board of Governors meeting in Vienna would be counterproductive.

"Resolutions, sanctions and threats have always made the issue more complicated," Soltanieh said.

The focus of the resolution drafted by the permanent UN Security Council members Britain, China, France, Russia and the United States, as well as Germany, was Iran's new enrichment plant at Fordu, near the city of Qom.

Due to Tehran's refusal to suspend its uranium enrichment programs, the United Nations Security Council has already passed four resolutions against Iran, three of them with sanctions.

Soltanieh earlier told the German daily Sueddeutsche Zeitung that Iran would reduce its co-operation with the IAEA to a minimum if a new resolution was issued against the Islamic state.

He, however, backed down in his remarks to IRNA, by calling on the UN nuclear watchdog "to let the process be continued in a calm and constructive atmosphere."

IAEA chief Mohamed ElBaradei on Thursday expressed disappointment with Iran and talked about a "dead end" as far as a breakthrough in the nuclear dispute with the country was concerned.