WASHINGTON -- The fate of talks in Geneva over Iran's nuclear program could rest on Capitol Hill.
That's where members of Congress were considering whether to push for additional sanctions against the Islamic republic, just as Tehran and the six world powers prepared to meet again.
U.S. lawmakers have of late heard two conflicting messages on how new sanctions could affect the outcome of what are widely considered to be the most promising round of negotiations since the Iranian nuclear crisis began.
Senior administration officials have warned that any new sanctions could derail the diplomatic track and lead to another conflict in the region. Pro-Israel groups and Congressional hawks, meanwhile, have argued that more sanctions could lead to a better deal with Iran.
The next round of talks in Switzerland between Iran and the so-called P5+1 -- the United States, Russia, China, Britain, France, plus Germany -- is set to begin on November 20.
John Hudson, national security reporter with "Foreign Policy," says it is not yet clear whether the Obama administration has managed to convince lawmakers to hold off on more sanctions.
"You've got a lot of work to do on the Senate Banking Committee, which is considering new sanctions on Iran that have been already been passed by the House regarding oil sales. Additionally, there is the risk that a number of senators are going to try to attach an amendment, anytime in the week, to the Senate [defense] authorization bill."
The National Defense Authorization Act could come before the Senate on the eve of the Geneva talks, although reports indicate that any effort to attach sanctions to the act would probably not be made until early December. Some Republican senators have said that sanctions attached to the bill would only take effect after three to six months, in order to give diplomacy a chance to work.
Supporters of new sanctions have argued that they give the U.S. more leverage in negotiations.
"I believe it's important for the United States to increase its negotiating leverage ahead of Geneva," says Mark Dubowitz, the director of the hawkish Foundation for the Defense of Democracies, which has been advising Congress on sanctions. "And it will be even more important for the United States to increase its negotiating leverage between any kind of interim deal reached and any kind of final deal."
Others have warned that any effort to tighten sanctions could undermine the talks with Iran.
Last week, the powerful chair of the Senate Intelligence Committee, Dianne Feinstein, indicated that she is "strongly" opposed to any attempt to increase sanctions while the talks are ongoing.
"Tacking new sanctions onto the defense authorization bill or any other legislation would not lead to a better deal," the senior Democratic senator from California said in a November 15 statement. "It would lead to no deal at all."
Feinstein said she was "baffled by the insistence of some senators to undermine" the talks.
Republican Senator John McCain, a leading critic of the U.S. policy toward Iran, has said that although he is "highly" skeptical of talks with Iran, he is willing to give the administration a few months before supporting new sanctions.
But four other Republican senators -- Mark Kirk of Illinois, Marco Rubio of Florida, John Cornyn of Texas, and Kelly Ayotte of New Hampshire -- have called for the intensification of sanctions against Iran.
"Rather than forfeiting our diplomatic leverage, we should increase it by intensifying sanctions until Iran suspends its nuclear and ballistic missile programs in accordance with multiple Security Council resolutions," the four senators wrote in a November 15 letter to U.S. President Barack Obama.
Obama met on November 19 with Senate leaders and the chair and ranking members of the Senate's banking, foreign relations, armed services, and intelligence committees to brief them on the talks with Iran and make his case. He was said to have repeated the message he delivered last week, when he urged Congress not to pursue new sanctions while the negotiations over Tehran's nuclear work were ongoing.
"If we're serious about pursuing diplomacy then there's no need to add new sanctions on top of the sanctions that are already very effective," Obama said.
The U.S. president added that if Iran fails to deliver on its promises, the sanctions "can be ramped back up."
According to Alireza Nader, a senior Iran analyst at the Rand Corporation, new sanctions could damage U.S efforts to roll back Iran's nuclear program.
"In the last round, Iran and the P5+1, including the United States, were very close to signing an agreement," he says. "This is the closest we've been to finding an agreement with Iran on the nuclear issue, probably for the past decade, and Iran has demonstrated seriousness in a negotiated settlement. At this point if Congress passes sanctions, it would demonstrate that the United States is not serious in a negotiated settlement."
Nader adds that, just because sanctions brought Iran to the negotiation table, it doesn't mean they will keep them there.
In Tehran, a political analyst who asked not to be named said more sanctions would give Iran the message that the United States was more interested in confrontation than agreement.
"[Iran's Supreme Leader Ayatollah Ali] Khamenei has called for 'heroic flexibility,'" the analyst said. "If the U.S. pushes for more sanctions then it could put an end to the establishment's willingness to be flexible, and it would undermine [Iranian President Hassan] Rohani's efforts to solve this issue."
On November 17, Mohammad Hossein Asafari, a member of the Iranian parliament’s National Security Committee, said Tehran would walk away from the negotiating table if Congress passed more sanctions.