European diplomats say Iran is considering suspending its uranium enrichment program for up to two months.
European Union negotiators said Iran's chief nuclear negotiator, Ali Larijani, proposed the suspension during talks in Vienna Sunday.
But the French news agency, AFP, quoted a member of the Iranian delegation, Ali Asghar Soltanieh, as denying that Iranian negotiators had offered any suspension.
When asked about the reports, White House spokesman Tony Snow said U.S. officials are still trying to understand the Iranian position.
European and Iranian negotiators have reported some progress in the talks, which may be Tehran's last chance to avoid international sanctions for its nuclear program.
The United States is pressing for sanctions to punish Iran for defying an August 31 U.N. deadline to suspend uranium enrichment.
Washington says it expects the U.N. Security Council to begin working in the coming days on a resolution authorizing sanctions against Iran.
But China and Russia, two permanent members of the Council, have been reluctant to punish Iran.
The U.S. and other Western nations have accused Iran of enriching uranium for developing nuclear weapons.
Iran has says its nuclear activities are for peaceful uses.
Some information for this report was provided by AFP, AP and Reuters.