WASHINGTON (CNN) -- The existence of a second uranium enrichment facility in Iran came to light on Friday, prompting President Obama and the leaders of Britain and France to publicly chide the Islamic republic and threaten further sanctions.

But the United States has actually known about the unfinished site since the Bush administration, according to senior U.S. officials who declined to be identified because of the sensitive nature of the negotiations. French intelligence officials were also aware of the facility for several months at least, a U.S. diplomatic source told CNN.

It wasn't until Monday that Iran wrote a letter to the International Atomic Energy Agency, revealing the existence of the underground facility on a military base near the city of Qom...