Hours later, Iran's nuclear chief told state TV that his country would allow the U.N. nuclear agency to inspect Iran's newly revealed and still unfinished uranium enrichment facility. Ali Akbar Salehi didn't specify when inspectors from the International Atomic Energy Agency could visit. He said the timing would be worked out with the U.N. watchdog.
The White House responded to the development by urging Iran's complete and immediate cooperation with the IAEA. "After hiding this site from the international community for years, full transparency is essential, and it is time for Iran to play by the rules like everyone else," White House spokesman Tommy Vietor said.
Obama said in his address that evidence of Iran's building the underground plant "continues a disturbing pattern of Iranian evasion" that jeopardizes global nonproliferation.
Ahead of Thursday's international talks with Iran in Geneva, Obama said the world "is more united than ever before" on this issue. Those negotiations, he said, "now take on added urgency."
Iran's failure to comply with international inspectors raised the potential of tougher economic penalties, although Obama and administration officials did not rule out military action.
"My offer of a serious, meaningful dialogue to resolve this issue remains open," Obama said, urging Tehran to "take action to demonstrate its peaceful intentions."
Evidence of the clandestine facility was presented Friday by Obama and the leaders of Britain and France at the G-20 economic summit in Pittsburgh. The news overshadowed developments on regulating financial markets and reducing fossil fuel subsidies.
Soon after, Russian President Dmitry Medvedev, at his own news conference, urged Iran to cooperate, as did Chinese Vice Foreign Minister He Yafei. He, however, did not endorse penalties against Tehran.
At a news conference in New York, Iranian President Mahmoud Ahmadinejad said his country had done nothing wrong and Obama would regret his actions.
"What we did was completely legal, according to the law. We have informed the agency, the agency will come and take a look and produce a report and it's nothing new," he said.
Ahmadinejad said the plant - which Iranian officials say was reported to nuclear authorities as required - wouldn't be operational for 18 months. But he sidestepped a question about whether Iran had sufficient uranium to manufacture a nuclear weapon.