Vienna ? In a blow to Iran, the board of the U.N. nuclear agency on Friday overwhelmingly backed a demand from the U.S., Russia, China and three other powers that Tehran immediately stop building its newly revealed nuclear facility and freeze uranium enrichment.

Iranian officials shrugged off approval of the resolution by 25 members of the 35-nation board of the International Atomic Energy Agency. But the U.S. and its allies hinted of new U.N. sanctions if Tehran remains defiant.

The West said some time remained for Tehran to come around and accept a specific offer that would delay its ability to make a nuclear weapon as well as engage in broader talks with the ultimate goal of persuading it to mothball its enrichment program.

But that window of opportunity would not stay open indefinitely, officials said.

“The next stage will have to be sanctions if Iran doesn’t respond to what is a very clear vote from the world community,” British Prime Minister Gordon Brown said.

German Foreign Minister Guido Westerwelle said the resolution’s passage shows that “the international community still wants dialogue with Iran, but time is pressing.”

“Our hand is still held out,” he added. “I hope Iran will take it. Iran must know: our patience is not infinite.”

Iran argues its nuclear program is aimed at creating a peaceful nuclear energy network to serve its growing population.