The UN nuclear watchdog's governing body today voted overwhelmingly to censure Iran for developing a uranium-enrichment facility in secret.
The International Atomic Energy Agency also demanded that Tehran freeze the uranium-enrichment project immediately.
The resolution was passed by a 25-3 margin with six abstentions. It urges Iran to immediately halt construction of the Fordow uranium-enrichment plant, located in a mountain bunker near the city of Qom.
It also demands that Tehran clarify the original purpose of the Fordow facility and to confirm that Iran does not have any more hidden atomic facilities or clandestine plants for any purpose.
Supporters of the IAEA resolution included Russia and China, which have shied away from censuring Iran in the past.
Russian and Chinese support for the IAEA resolution sends Tehran a clear message of international exasperation about the secrecy and defiance surrounding its controversial nuclear program.
Russia and China both have the power to veto possible international sanctions as permanent members of the United Nations Security Council. But it was not immediately clear whether their support on today's IAEA measure would translate into crucial Russian-Chinese support for wider UN sanctions that Western leaders may push for.
The West is concerned that Iran is secretly trying to build nuclear weapons in violation of its obligations under the nuclear Non-Proliferation Treaty.
Those who voted against the censure measure -- Venezuela, Malaysia, and Cuba -- are all developing countries in a bloc with Iran. They called the resolution provocative and counterproductive.
The six countries that abstained from today's vote were Afghanistan, Brazil, Egypt, Pakistan, South Africa, and Turkey. Azerbaijan was the only country on the IAEA board whose representative was absent when today's vote was taken.
Iranian officials say the IAEA resolution will undermine its relations with the UN nuclear watchdog.
But supporters of the move say they were provoked by the revelation in September that Iran has been secretly building a second uranium-enrichment facility for at least two years -- a subterfuge they said had raised suspicions there may be more secret Iranian nuclear sites that could be dedicated to making atom bombs.
The IAEA measure also signals diminishing tolerance over Iran's reluctance to embrace an IAEA-brokered compromise deal on its enriched uranium.
That plan calls for Iran to ship its low-enriched uranium to Russia where it would be further enriched for use in a nuclear power station. It would then be shipped to France where it would be packaged in nuclear fuel rods and then sent back to Iran.
IAEA Director-General Muhammad el-Baradei told reporters in Vienna before the vote that Iran has continued to make counteroffers rather than accepting the compromise deal.
"[Iran's] position -- conveyed to me orally a number of times -- is that they want a simultaneous swap between the fuel and their low-enriched uranium," el-Baradei said.
"They are ready to put this material under IAEA control in an island in the Persian Gulf -- [the Iranian island of] Kish -- under our control and custody. But that will not take the material out [of Iran.] The whole idea, as I explained to them, to diffuse the crisis is to take the material out [of Iran]."
Tehran has repeatedly denied that it is trying to build nuclear weapons, claiming that its nuclear program is only for medical research and the peaceful production of nuclear energy.
Today's IAEA board meeting is the last under the leadership of el-Baradei, an Egyptian diplomat and 2005 Nobel Peace Prize laureate, who is due to step down as the IAEA director-general on November 30 after 12 years in the post.