VIENNA | 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.

FILE - In this Jan. 16, 2016 file-pool photo, Secretary of State John Kerry speaks in Vienna that sanctions will be lifted on Iran after the International Atomic Energy Agency (IAEA) verified that Iran has met all conditions under the nuclear deal. The Iran nuclear accord is fragile at its one-year anniversary. Upcoming elections in the U.S. and Iran could yield new leaders determined to derail the deal. The Mideast’s wars pit U.S. and Iranian proxies in conflict, with risks of escalation. Iran's ballistic missiles are threatening American allies in the Arab world and Israel, raising pressure on the United States to respond with force. (Kevin Lamarque/Pool via AP, File)

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.