PARIS -- Iran and six world powers have agreed on how to put in place an accord that would temporarily freeze much of Iran's nuclear program, U.S. and Iranian officials said Sunday.
That accord would go into effect Jan. 20.
International negotiators worked out an agreement in November to constrain much of Iran's program for six months so that diplomats would have time to pursue a more comprehensive follow-up accord.
But before the temporary agreement could take effect, negotiators had to work out the technical procedures for carrying it out and resolve some of its ambiguities in concert with the International Atomic Energy Agency.
Under the interim agreement, Iran would stop en
riching uranium beyond 5 percent, a level that would be sufficient for energy production but that would require further enrichment for making bombs.
Iran's stockpile of uranium enriched to 20 percent would be diluted or converted to oxide so that it could not be readily used for military purposes.
Iran agreed not to install any new centrifuges, start up any that were not already operating or build new enrichment facilities.
The agreement, however, does not require Iran to stop enriching uranium to a low level of 3.5 percent, or to dismantle any existing centrifuges.
In return, the United States and its negotiating partners will provide Iran with billions of dollars in relief from economic sanctions.
"Beginning Jan. 20, Iran will for the first time start eliminating its stockpile of higher levels of enriched uranium and dismantling some of the infrastructure that makes such enrichment possible," President Barack Obama said in a statement Sunday.
A major question now is whether this interim accord will set the conditions for a more far-reaching agreement that would substantially roll back Iran's program.
Critics have asserted that by providing Iran with $6 billion to $7 billion in sanctions relief, according to White House estimates, the West would be easing the pressure on the government to make major concessions. But defenders of the interim accord said that it was needed to maintain the support of the United States' negotiating partners and to buy time to pursue a comprehensive agreement.
At a conference in December held by the Saban Center for Middle East Policy, Obama said that there was no more than a 50-50 chance of achieving a more comprehensive follow-up accord.
In a statement issued in Paris, Secretary of State John Kerry said the negotiations on a follow-up agreement would be "difficult."
"We are clear-eyed about the even greater challenges we all face in negotiating a comprehensive agreement," said Kerry, who is in Paris for a meeting on the Syrian crisis. "These negotiations will be very difficult, but they represent the best chance we have to resolve this critical national security issue peacefully, and durably."