On the same day President Obama warned the Islamic Republic to cooperate after the discovery of a covert nuclear facility or face action by the world's nations, Iran's nuclear chief said his country will allow the U.N. nuclear agency to inspect its newly revealed, still unfinished uranium enrichment facility.

Ali Akbar Salehi didn't specify when inspectors from the International Atomic Energy Agency could visit the site, saying simply the timing will be worked out with the U.N. watchdog.

Iran's newly revealed site is said to be in the arid mountains near the holy city of Qom, inside a heavily guarded, underground facility.

The pilot plant will house 3,000 centrifuges that could soon produce nuclear fuel -- or the payload for atomic warheads. Salehi spoke on state TV Saturday.

He says Iran has "pre-empted a conspiracy" against Tehran by the U.S. and its allies by reporting the site voluntarily to the IAEA.

In his weekly radio and Internet address, Obama said that evidence showing Iran building an underground plant to enrich uranium that could be used for an atomic bomb "continues a disturbing pattern of Iranian evasion" that jeopardizes global nonproliferation.

He urged Tehran once again to open the site to international inspectors, or face consequences. The chief option is tougher economic sanctions, but on Friday 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. "But Iran must now cooperate fully with the International Atomic Energy Agency, and take action to demonstrate its peaceful intentions."

"Iran's leaders must now choose -- they can live up to their responsibilities and achieve integration with the community of nations. Or they will face increased pressure and isolation, and deny opportunity to their own people."

Israeli Foreign Minister Avigdor Lieberman says Iranian nuclear facility proves the Islamic Republic is pursuing nuclear weapons.

Lieberman told Israel radio on Saturday that "without a doubt" the reactor was for military purposes.

Israel considers Iran a strategic threat due to its nuclear program, missile development and repeated references by Iranian President Mahmoud Ahmadinejad to Israel's destruction.

Meanwhile, an aide to Iran's Supreme Leader Ayatollah Ali Khamenei was quoted as saying Saturday that the newly disclosed facility will soon become operational. 

"This new plant, God willing, will soon become operational and will make the enemies blind," Mohammad Mohammadi-Golpayegani, who heads Khamenei's office, said, according to the semi-official Fars News Agency.

Evidence of the clandestine facility was unveiled Friday by Obama and the leaders of Britain and France at the G-20 economic summit in Pittsburgh, where it 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 sanctions against the country.

"On this, the international community is more united than ever before ... that Iran must fulfill its responsibilities," Obama said.

Iran, so far, hasn't budged.

At a news conference in New York, Ahmadinejad said his country had done nothing wrong and Obama would regret his actions.

Ahmadinejad sidestepped a question about whether Iran had sufficient uranium to manufacture a nuclear weapon.

The head of Iran's nuclear program suggested that U.N. inspectors may be allowed to visit the site. Ali Akbar Salehi called the incomplete facility "a semi-industrial plant for enriching nuclear fuel," but he gave no other details, according to the state news agency IRNA.

Obama, and other world leaders, will be looking to see where Iran stands next week during a meeting of major nations on the nuclear issue.

Obama said Saturday the negotiations have taken on added urgency.

The Associated Press contributed to this report.