Iran has told the U.N. nuclear watchdog that it has a second uranium enrichment plant under construction, a belated disclosure sure to heighten Western fears of a stealthy Iranian quest for nuclear arms capability.

Iran told the International Atomic Energy Agency of the plant's existence in a letter to IAEA Director-General Mohamed ElBaradei on Monday just as six world powers and Iran prepare for rare talks on October 1 on its disputed nuclear drive...

...A senior White House official said President Barack Obama and the leaders of Britain and France, now at a G-20 summit of industrialized nations in Pittsburgh, would accuse Iran on Friday of concealing a sensitive plant from the IAEA for years.

Obama would demand that Iran allow an immediate IAEA inspection of the plant, the official said.

He said the nascent plant was believed to be designed for about 3,000 centrifuges for enriching uranium, nominally enough machines to produce material for one nuclear device in a year if run nonstop, although Iran does not appear to have mastered the sophisticated technology consistently yet, nuclear analysts say...