In recent months, Iran has begun installing at nuclear sites hundreds of more-advanced centrifuge machines capable of producing fuel at three times the current rate, according to U.S. and U.N. officials.

WSJ: Kerry Focuses on Iran, North Korea Leaders

In recent months, Iran has begun installing hundreds of more advanced centrifuge machines at nuclear sites, which are capable of producing fuel at three times the current rate, according to U.S. and U.N. officials.

WSJ: Kerry Focuses on Iran, North Korea Leaders

"The Secretariat of the Agency received a letter from the Atomic Energy Organization of Iran (AEOI) dated 23 January 2013 informing the Agency that 'centrifuge machines type IR2m will be used in Unit A-22' at the Fuel Enrichment Plant (FEP) at Natanz, " the IAEA communication is reported to say.

BBC: Natanz uranium enrichment plant