New revelations about Iran's nuclear ambitions were center stage at the G-20 Summit in Pittsburgh today, where President Obama, French President Nikolas Sarkozy and British Prime Minister Gordon Brown said Iran has until December to reverse course or face stiff international sanctions.
Sarkozy said that "if by December there is not an in-depth change by the Iranian leaders, sanctions will have to be taken."
Obama called evidence of Iran's second, secret underground nuclear fuel plant a "direct challenge" to the principles of nuclear nonproliferation.
"Iran has a right to peaceful nuclear power that meets the energy needs of its people," Obama said. "But Iran is breaking rules all nations must follow. ... It's time for Iran to act immediately to restore the confidence of the international community by fulfilling its international obligations.
There were three main reasons officials concluded the secret site was built to manufacture fuel for nuclear bombs, U.S. officials told ABC News.
First, though they were shown in satellite imagery, it was clear a facility was being constructed underground and heavily disguised.
Second, satellites showed the site was built on a military base and protected by armed guard around the clock.
Third, intelligence that may include spies on the ground shows the facility is designed to hold only about 3,000 centrifuges to enrich uranium, which is not enough to fuel a civilian power plant. That would need more like 50,000 centrifuges.
"It is very strong circumstantial evidence that Iran's intentions are to build a weapon," said Joe Cirincione, president of Ploughshares Fund, a foundation dedicated to security and peace funding.
The United States also has been gathering additional evidence -- including the comings and goings of equipment and suspect personnel, sources said.
Perhaps most damning is Iran's history. The nation has been working on a nuclear program since the 1980s, and has been accused of lying about it repeatedly.
President Obama said Iran "must be prepared to cooperate fully" at the upcoming Oct. 1 meeting between Iranian officials and representatives of the five permanent members of the United Nations Security Council -- the U.S., Russia, China, U.K. and France -- plus Germany.
Obama said at that meeting Iran must "demonstrate that it is committed to establishing its peaceful intentions through meaningful dialogue and concrete actions."
In the meantime, Sarkozy said the "exceptional" new findings necessitate an "exhaustive, strict and rigorous investigation" by the IAEA.
"Everything, everything must be put on the table now," Sarkozy said. "We cannot let the Iranian leaders gain time while the motors are running."
Brown reiterated a sense of urgency, saying "the international community has no choice today but to draw a line in the sand. ... America, the United Kingdom, and France are one."
He said the "level of deception" by Iran in keeping its second nuclear site secret will "shock and anger the whole international community and harden our resolve."
In an exclusive meeting with Time magazine this morning as Obama, Sarkozy and Brown delivered their remarks, Iranian President Mahmoud Ahmedinejad called Obama's statement "definitely a mistake."