President Barack Obama has known about the secret site where Iran has established a unranium enrichment facility for nearly a year.
According to The New York Times, Obama was informed of the site in Qom, Iran, by Bush administration officials at some point after his election last November.
Earlier this year sensitive equipment was moved to the site, prompting Obama to reveal its existence on Friday night at the G-20 economic summit in Pittsburgh. On Saturday, Obama issued an ultimatum to Iran:
"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," he said in his radio and Internet address.
Obama said the construction of the underground plant at Qom "continues a disturbing pattern of Iranian evasion."
Iran says the facility is intended for peaceful purposes only, but the United States fears it will be used to produce highly enriched nuclear material for a bomb.