The United Nations nuclear watchdog's governing board voted overwhelmingly yesterday to censure Iran for its defiant nuclear policies, and demanded an immediate halt to work on an uranium-enrichment plant built in secret in mountain tunnels south of the Iranian capital.

The declaration criticizing Iran - approved 25 to 3 by the 35-nation board, with six countries abstaining and one not present - was quickly condemned by Iranian officials who called the resolution "a historic mistake" and threatened to curtail its cooperation with the International Atomic Energy Agency.

The resolution represented a rare show of global solidarity against Iran's nuclear program, drawing support not only from Western powers but also from Russia and China. Cuba, Malaysia and Venezuela opposed the measure.

"Our patience and that of the international community is limited," Glyn Davies, the U.S. envoy to the U.N. agency, said following the vote at the IAEA's Vienna, Austria, headquarters. Obama administration officials had lobbied intensively to ensure strong backing for the resolution as a prelude to a possible fourth round of U.N. sanctions against the Islamic republic.

The largely symbolic resolution berates Iran for its continued defiance of U.N. resolutions that demand a halt to uranium enrichment and other activities that U.S. officials believe are aimed at developing nuclear weapons. The declaration is particularly critical of Iran's secret construction of a second enrichment plant inside mountain bunkers near the ancient city of Qom, southwest of Tehran.

Iran says it wants nuclear power only to make electricity.

Iran's failure to notify the IAEA of the project was a "breach of its obligation" under U.N. treaties, the resolution states. The most sweeping criticism of Iran's nuclear program by the watchdog group in nearly four years, the resolution will be referred to the U.N. Security Council, which has the authority to enact tougher sanctions.

In Washington, White House press secretary Robert Gibbs hailed the vote as underscoring a commitment by the international community "to enforce the rules of the road, and to hold Iran accountable to those rules."

"If Iran refuses to meet its obligations, then it will be responsible for its own growing isolation and the consequences," Gibbs said.

Iran's representative to the IAEA, Ali Asghar Soltanieh, suggested that Iran would stop some of its voluntary cooperation with the agency, according to a report yesterday by the semi-official Fars news agency. "This resolution is a historic mistake by those who designed it," Soltanieh was quoted as saying.

It was unclear what specific steps, if any, the government would take in response. Iranian analysts said that the government probably would not withdraw completely from the Non-Proliferation Treaty, which requires states to submit to international inspections, or shut down cameras that allow the IAEA to monitor activities at nuclear facilities in Iran. The analysts said Iran might stop providing certain technical information about future plans for new nuclear sites, or make it more difficult for IAEA inspectors to obtain visas.

"I don't believe they will go as far as taking down the cameras. It is not in our interest to stop cooperation on critical trust building issues," said an Iranian analyst who is close to former nuclear negotiators, speaking on condition of anonymity.

Soltanieh, in a statement reported by state-run Iranian television, declared that "neither sanctions nor the threat of military attacks can interrupt our peaceful nuclear activities even for a second." He accused the United States and other Western powers of attempting to "spoil the positive atmosphere" his country enjoys with U.N. nuclear inspectors. But his description of relations with the IAEA were at odds with comments Thursday by Mohamed ElBaradei, the atomic agency's director general, who retires from the post next week.

ElBaradei, repeating a complaint he has made frequently over the past year, criticized Iran for failing to properly answer IAEA questions about leaked documents that suggest that Iran was performing secret research on nuclear warheads at least as recently as 2003.

"There has been no movement on remaining issues of concern which need to be clarified for the agency to verify the exclusively peaceful nature of Iran's nuclear program," ElBaradei told a session of the governing board. "We have effectively reached a dead end, unless Iran engages fully with us."