By GEORGE JAHN, Associated Press

VIENNA (AP) — A document obtained by The Associated Press shows that key restrictions on Iran's nuclear program will ease in slightly more than a decade, halving the time Tehran would need to build a bomb.

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The document is the only secret text linked to last year's agreement between Iran and six foreign powers. It says that after a period between 11 to 13 years, Iran can replace its 5,060 inefficient centrifuges with up to 3,500 advanced machines.

Since those are five times as efficient, the time Iran would need to make a weapon would drop from a year to six months.

Iran says its enrichment is peaceful, but the program could be used for nuclear warheads.

Two diplomats providing the information Monday demanded anonymity because they weren't authorized to do so.