Speaking in an early-morning joint appearance with British Prime Minister Gordon Brown and French President Nicolas Sarkozy at a Group of 20 summit in Pittsburgh, President Barack Obama accused Iran of building a secret nuclear fuel plant for several years and demanded that Tehran comply with international rules on nuclear nonproliferation.
President Obama called Iran's activities "a direct challenge" to the nuclear nonproliferation regime and said it was time for Tehran to act immediately to restore the confidence of the international community.
Sarkozy said Iran was going down a "dangerous" path and threatened new sanctions if Iranian leaders did not change course by December.
Iran revealed the existence of the plant to the United Nations watchdog on Monday, saying it was not yet operational and would only be used for nuclear energy.
The Iranian government is under three sets of U.N. Security Council sanctions for refusing to freeze enrichment at what had been its single known enrichment plant, which is being monitored by the IAEA.
Speaking after President Obama, the French and British leaders used strong language to insist that Iran would now have to disclose full details of its entire nuclear program or face new and tougher sanctions.
Brown stressed that the United States, France and Britain were "at one" on the issue, and accused the Iranians of "serial deception."
"The level of deception by the Iranian government ... will shock and anger the whole international community, and it will harden our resolve," Brown said, adding that it's time "to draw a line in the sand."
Two Iranian officials told the Associated Press that their government revealed the existence of the second plant in a letter sent Monday to IAEA chief Mohamed El-Baradei.
IAEA spokesman Marc Vidricaire confirmed to the AP receiving the letter, saying the agency was informed "that a new pilot fuel enrichment plant is under construction." The letter said that the plant would not enrich uranium beyond the 5 percent level suitable for civilian energy production. That would be substantially below the threshold of 90 percent or more needed for a weapon.
Iran told the agency "that no nuclear material has been introduced into the facility," Vidricaire said. "In response, the IAEA has requested Iran to provide specific information and access to the facility as soon as possible."
Iran's president, Mahmoud Ahmadinejad, made no reference to the new facility while attending the U.N. General Assembly in New York this week, but asserted in a speech that his country had fully cooperated with international nuclear inspectors.
The officials said that Iran's letter contained no details about the location of the second facility, when -- or if -- it had started operations or the type and number of centrifuges it was running.
But one of the officials, who had access to a review of Western intelligence on the issue, told the AP it was about 100 miles southwest of Tehran and was the site of 3,000 centrifuges that could be operational by next year.
Iran says it has the right to enrich uranium for a nationwide chain of nuclear energy reactors. But because enrichment can also produce weapons-grade uranium, the international community fears Tehran will make fissile material for nuclear warheads.
The revelation of a secret plant further hinders the chances of progress in scheduled Oct. 1 talks between Iran and six world powers.
At that meeting -- the first in more than a year -- the five permanent U.N. Security Council members and Germany plan to press Iran to scale back on its enrichment activities. But Tehran has declared that it will not bargain on enrichment
Sarkozy said Friday the situation was a challenge to the entire international community.
"Everything must be put on the table," the French president said.
---- Compiled from wire reports and other media sources