Secretary of State Condoleezza Rice said Friday the United States is willing to look at creative ways to get Iran to halt nuclear activities that could lead to a bomb. She held firm that the U.S. won't discuss rewards for Iran until it meets that condition.

The top U.S. diplomat signaled support for a behind-the-scenes effort to strike a technical and semantic compromise that could allow Iran to stop, or suspend, disputed activities and open the door for international negotiations.

"Where we've been flexible is on how we get to suspension," Rice told reporters one day after inconclusive talks between European and Iranian nuclear negotiators.

The U.N. Security Council has demanded that Iran at least temporarily suspend its enrichment of uranium, an ingredient both for nuclear energy or nuclear weapons, before talks on a package of incentives could begin.

"Where we have been flexible is on myriad ways that a consultation process could lead the Iranians to a position where they could suspend," Rice said.

She said she saw no evidence that Thursday's talks in Madrid produced any momentum, but noted that the two negotiators had agreed to met again in two weeks. Rice spoke to reporters as she flew from Berlin to Madrid for a visit unrelated to the nuclear talks.

Meanwhile, in what appeared to be an attempt to delay the threat of new U.N. sanctions, Iran pledged on Thursday to cooperate with the nuclear monitoring agency probing its atomic program, according to an official speaking to The Associated Press. That would end years of stonewalling by Iran and help the International Atomic Energy Agency establish whether Tehran's past nuclear efforts were exclusively peaceful in nature. U.N. and other officials, who demanded anonymity because they were not authorized to discuss the issue, said Friday a decision by Iran to help clear up past activities would represent a major concession.

Suspension of nuclear efforts is an inexact term, both for diplomats and the U.N.'s nuclear experts, and analysts said it leaves negotiators some wiggle room. Iran has not seemed publicly interested, but European diplomats have sought some middle ground.

The United States wants the suspension to become permanent, leaving Iran unable to develop weapons but theoretically able to operate nuclear power stations with uranium processed offshore by others. The complicated, multistep process of manufacturing nuclear-ready uranium is called the fuel cycle.

"The issue is that any Iranian civilian nuclear program really can't have the fuel cycle attached to it, or the ability to perfect that technology," Rice said, something that could be worked out once Iran sat down for detailed talks.

The United States agreed to join any such talks last year on condition that Iran stop its disputed uranium work, but Iran has refused. Work has gone ahead rapidly in Iran during a two-year diplomatic deadlock.

"What we can't do is to have negotiations take place while the Iranians continue to perfect their nuclear technology and use those negotiations as cover," for possibly covert work on a bomb, Rice said. "That's what we can't accept."