VIENNA (Reuters) - The U.N. nuclear watchdog voted Friday to rebuke Iran for building a uranium enrichment plant in secret but Tehran rejected the move as "intimidation" which would poison its negotiations with world powers.
The resolution was the first by the 35-nation board of the International Atomic Energy Agency (IAEA) against Iran in almost four years, and a sign of spreading alarm over Tehran's failure to dispel fears it has clandestine plans to build nuclear bombs.
It passed by a 25-3 margin with six abstentions, smoothed by rare backing from Russia and China, which have blocked global attempts to isolate Iran, a trade partner for both, in the past.
But it was far from clear whether the West could now coax Moscow and Beijing to join in biting sanctions against Iran, something they have long prevented at the U.N. Security Council.
Russia's Foreign Ministry said Iran should "react with full seriousness to the signal contained in the resolution ... and to ensure full cooperation with the agency."
Moscow and Beijing's support is seen as vital to the success of external pressure on Iran to rein in its nuclear activity and open it up to unfettered IAEA inspections and investigations.
The vote reflected exasperation with Iran's retreat from an IAEA-brokered draft deal to provide it with fuel for a medical nuclear reactor if it agreed to part with its enriched uranium, which could be turned into bomb material if further refined.
British Prime Minister Gordon Brown said major powers would pursue harsher sanctions against Iran if it ignored the vote.
British Foreign Secretary David Miliband "should send a very clear warning to Iran that it is not going to be able to divide the international community," Miliband told Reuters in an interview at a Commonwealth summit in Trinidad and Tobago.
The resolution urged Iran to clarify the original purpose of the Fordow enrichment site, hidden inside a mountain bunker, stop construction and confirm there are no more hidden sites.
Iran said those demands were beyond its legal obligations.
The United States said the IAEA vote showed an urgent need for Iran to address the growing "deficit of confidence" over its nuclear intentions. Time is running out, the White House said, and Iran would be responsible for the consequences.
The measure won blanket Western backing. Cuba, Malaysia and Venezuela, prominent in a developing nation bloc that includes Iran, voted "no," while Afghanistan, Brazil, Egypt, Pakistan, South Africa and Turkey abstained. Azerbaijan missed the ballot.
Diplomats said the large number of abstentions indicated important developing states were souring on Iran over its nuclear defiance, particularly its hold-up of the fuel deal.
But, they said, the IAEA resolution could lead Iranian hardliners to seize on it as excuse to restrict inspections further and re-freeze talks, killing off the reactor fuel plan.
The Islamic Republic has counted on Non-Aligned Movement solidarity to help prevent a united front against it.
Israel sees Iran's nuclear program as an existential threat given Iranian comments calling for the destruction of the Jewish state and has not ruled out military strikes against the sites. It said the IAEA resolution was of "great importance."
Israel's Foreign Ministry called for the international community to ensure the decision bore a "practical significance by setting a timetable to require the imposition of stiff sanctions against Iran in response to any violations."
Iran denies seeking nuclear weapons, saying its atomic energy program is purely for peaceful purposes. But its record of clandestine nuclear work and curbs on IAEA inspections have stoked suspicions and a seven-year standoff with world powers.
Iranian Ambassador Ali Asghar Soltanieh called the resolution a "hasty and undue" step devoid of legal basis.
"The great nation of Iran will never bow to pressure and intimidation vis-a-vis its inalienable right to peaceful uses of nuclear energy," he said.
"We will not implement any word of it because this is a politically motivated gesture against the Iranian nation."
He said Iran would continue to allow basic inspections at its nuclear sites but could stop making "voluntary gestures" of extra cooperation such as when it allowed widened surveillance at its rapidly expanding main enrichment complex at Natanz.
Soltanieh said the resolution would also ruin the atmosphere for further talks with the United States, France, Britain, Germany, Russia and China launched on October 1 in Geneva, where the reactor fuel plan was agreed in principle.
"Such gestures ... are certainly destructive. They spoil the existing cooperative environment. But neither sanctions nor the threat of military attacks can interrupt our peaceful nuclear activities even for a second," he said.
Iran admitted Fordow's existence in September, at least two years into its construction, shocking IAEA inspectors. Western diplomats said Iran was forced to come clean after learning the site had been detected by their spy services.
Iran had assured the IAEA last year it was not hiding any nuclear-related activities despite rules that it be transparent.
Fordow's emergence fanned suspicions there are more secret sites intended to produce atom bombs, since experts said the plant's capacity was too small to feed a civilian nuclear power plant, but big enough to make weapons material.
Iran's main, larger enrichment plant, at Natanz, was exposed by Iranian opposition exiles in 2002.
Iran has told the IAEA it developed the Fordow site in secret as a backup for other, known facilities, in case they were bombed by Israel.
The last IAEA board resolution against Iran was in February 2006, when governors referred Tehran's dossier to the U.N. Security Council over its refusal to shelve enrichment.
Additional reporting by Sylvia Westall in Vienna, Adrian Croft in Trinidad, Sophie Hardach in Paris and David Alexander in Washington; editing by Jon Hemming and Todd Eastham