Supreme Leader Ayatollah Ali Khamenei has ensured Iranian nuclear officials keep the country's amount of uranium enriched to 20 percent purity below 250 kilograms, or about 551 pounds, the senior officials told The Wall Street Journal in a story published Tuesday.
The 250-kilogram amount of uranium enriched to 20 percent purity is what experts say Iran would need to make an atomic bomb if it processed the uranium further into weapons-grade fuel.
It is also the amount Israeli Prime Minister Binyamin Netanyahu told the United Nations in September was the "red line" the world should prevent Iran from crossing, through military action if necessary.
U.S. and Israeli officials told the Journal they believed Iran's moves to stay clear of 250 kilograms were a stalling tactic, rather than a change of direction for the nuclear program, which Iran insists is simply developing civilian nuclear power -- a claim Washington and Jerusalem say they do not believe.
The U.S. and Israeli officials cited by the Journal pointed to other Iranian actions that are accelerating the pace at which Tehran could create weapons-grade fuel. One action involves thousands of centrifuge machines the U.N. nuclear watchdog, the International Atomic Energy Agency, reported were installed at the deep-underground Fordo uranium-enrichment plant south of Tehran, near the holy city of Qom.
Fordo is in a fortified bunker seen as largely immune to U.S. or Israeli military strikes, the Journal said.
International negotiations aimed at containing Iran's nuclear program are to resume Friday in Kazakhstan. The talks, involving the five permanent U.N. Security Council members plus Germany, are expected to be the last round of diplomacy with Tehran until after the June elections, U.S. officials said.
The officials expressed doubts any big breakthrough would come about in Kazakhstan, in part because Khamenei, 73, is focused on the June elections -- specifically on getting a leader more aligned with his positions than outgoing Iranian President Mahmoud Ahmadinejad.
Khamenei -- who Iranian officials say is the ultimate decision maker on Iran's diplomacy and nuclear program -- supported Ahmadinejad at the start but now wants someone more malleable, the Journal said.
Ahmadinejad challenged Tehran's political elite and worsened Iran's economic ills by spending lavishly on populist development projects, the Journal said.
Khamenei may be eyeing his personal representative to the nuclear talks, Saeed Jalili, as an Ahmadinejad successor, political analysts cited by the Journal said.