A senior U.S. administration official says Iran and world powers will begin drafting a comprehensive nuclear agreement next month.
Speaking to journalists on April 4, the official said the sides were making progress in talks over Tehran’s disputed nuclear program.
He made the comments ahead of a new round of negotiations in Vienna on April 8-9.
Iran and the six powers reached an interim deal in Geneva in November.
Under the accord, Tehran agreed to freeze some nuclear activities for six months in exchange for partial sanctions relief.
The U.S. official also said on April 4 that the United States had no information suggesting that an oil-for-goods deal between Iran and Russia has been implemented or finalized.
Reuters reported on April 2 that Russia and Iran had made progress toward an oil-for-goods agreement that could enable Tehran to boost energy exports in defiance of sanctions.
The U.S. official said that if such a deal were to happen, it could trigger U.S. sanctions against entities and individuals involved.
"We've been very clear about our concerns with both parties regarding this or any similar deal," the official said.
He added that such deal would be "inconsistent" with the terms of Iran's agreement with world powers on its nuclear program.