(Analyst's note:  IAEA, Mohamed ElBaradei admits failure. )

The UN nuclear watchdog's governing body has passed a resolution condemning Iran for developing a uranium enrichment site in secret.

The International Atomic Energy Agency (IAEA) also demanded that Iran freeze the project immediately.

The resolution, the first against Iran in nearly four years, was passed by a 25-3 margin with six abstentions.

Iran says its nuclear programme is for peaceful energy purposes, but the US says it is seeking nuclear weapons.

In September, it emerged that as well as its uranium enrichment facility at Natanz, Iran had a second such facility near the town of Qom. The revelation deepened Western fears about the country's nuclear ambitions.

The IAEA resolution was passed with rare Russian and Chinese backing.

Speaking at a Commonwealth summit in Trinidad and Tobago, British Prime Minister Gordon Brown said that the vote sent "the clearest possible signal to Iran that they should desist from their nuclear plans, that the world knows what they are doing".

It comes a day after the outgoing head of the IAEA, Mohamed ElBaradei, expressed frustration at Iran's refusal to accept an international proposal to end the dispute over its nuclear programme.

The plan envisages Iran's low-enriched uranium being shipped overseas for processing into fuel. This is seen as a way for Iran to get the fuel it wants, while giving guarantees to the West that it will not be used for nuclear weapons.

Iran's ambassador to the IAEA, Ali Asghar Soltanieh, said the resolution was a "hasty and undue" step that would jeopardise the chances of success of the talks on the proposal.

The US ambassador to the nuclear watchdog, Glyn Davies, said patience with Iran was "running out" but insisted that the resolution was "not meant to be punitive".

"I hope it provides further impetus on the diplomatic track," he added.

Addressing IAEA governors in Vienna on Thursday, Mr ElBaradei said his inspectors had made no progress in their attempts to verify the peaceful nature of Iran's nuclear programme.

"It is now well over a year since the agency was last able to engage Iran in discussions about these outstanding issues," he said. "We have effectively reached a dead end, unless Iran engages fully with us."