For the U.S. and its allies, low-enriched uranium is problematic because it can also be used to arm nuclear weapons, albeit the process is longer and more complicated than for 20 percent uranium.
While seeking only to reduce enrichment at a sprawling underground facility at Natanz, the six powers also want complete closure of another enrichment plant at Fordo south of Tehran. The Fordo site is heavily fortified, making it more difficult to destroy than Natanz if it turns toward making nuclear weapons.
Demands to reduce enrichment instead of stopping it implicitly recognize Iran's right to enrich for peaceful purposes. That already is a victory for Tehran, considering talks began 10 years ago with the international community calling on the Islamic Republic to mothball its enrichment program.
"It's pretty clear that Iran will have to be allowed some degree of enrichment," said former U.S. State Department official Mark Fitzpatrick, who now is a director at the International Institute for Strategic Studies. "But the enrichment has to be limited."
That could be a tough sell politically in the U.S. and Israel.
In a letter to President Barack Obama, 10 leading U.S. senators — six Democrats and four Republicans — insisted that Iran must end all uranium enrichment. Israeli Prime Minister Benjamin Netanyahu told his parliament Monday that the international community must maintain firm pressure on Iran until it quits enriching uranium.
The former U.N. official also said that his talks with senior Iranian officials indicate there will be tough bargaining on centrifuge numbers.
Even if Tehran agrees to downsize enrichment, the Iranians will probably offer stiff resistance to closing Fordo, he added summarizing his talks with senior Iranian officials directly involved in the upcoming negotiations.
Associated Press Vienna bureau chief George Jahn has covered Iran's nuclear program since 2003.
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