The White House warned Congress that passing new sanctions on Iran -- even with a delayed launch date -- would give Tehran an excuse to undermine an interim nuclear deal.
White House spokesman Jay Carney also warned a bipartisan coalition of senators who are suspicious of the pact reached last month and want to pile up more punishments for Tehran, that their move would be seen as a show of "bad faith" by US partners abroad.
The White House stepped up its rhetorical push to forestall new sanctions amid intense behind-the-scenes lobbying by top Obama administration officials targeting key lawmakers from both Democratic and Republican parties.
"Passing any new sanctions right now will undermine our efforts to achieve a peaceful resolution to this issue by giving the Iranians an excuse to push the terms of the agreement on their side," Carney said.
"Furthermore, new sanctions are unnecessary right now because our core sanctions architecture remains in place, and the Iranians continue to be under extraordinary pressure.
"If we pass sanctions now, even with the deferred trigger, which has been discussed, the Iranians and likely our international partners will see us as having negotiated in bad faith."
Carney argued that the passage of new US sanctions -- even with a built-in six-month delay contemplated by hawks on Capitol Hill -- would threaten the unity of the international coalition that has leveled punishing sanctions on Tehran.
He also said if the interim deal -- which freezes aspects of Iran's nuclear program in return for a slight easing of the sanctions that have crippled the country's economy -- is not translated into a final pact that Iran abides by, the White House would support new sanctions against the Islamic Republic.
Barack Obama's domestic opponents have seized on the terms of the deal to claim that it enshrines the right of Iran to enrich uranium but the White House late Tuesday issued a statement which sought to clarify the scope of any eventual final nuclear deal with Tehran.
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Bernadette Meehan, a National Security Council spokeswoman, said that the United States did not recognize that Iran has "a right to enrich" and that such a right was not included in the deal reached between Iran and six world powers in Geneva last month.
"We are prepared to negotiate a strictly limited enrichment program in the end state, but only because the Iranians have indicated for the first time in a public document that they are prepared to accept rigorous monitoring and limits on scope, capacity, and stockpiles," she said.
"If we can reach an understanding on all of these strict constraints then we could have an arrangement that includes a very modest amount of enrichment that is tied to Iran's practical needs and that eliminates any near-term breakout capacity."
Breakout capacity is the time needed for Iran to manufacture a nuclear bomb if it decided to do so.
US intelligence assessments suggest that the Islamic Republic's leaders have yet to take such a step.
While some reports billed the White House statement as a major concession on enrichment, Obama has all along argued that his aim in the negotiations is to ensure that Iran does not develop a nuclear weapon and that Tehran could retain some verifiably peaceful civilian nuclear program.
By implication, that means Iran could end up with some limited capacity to enrich, albeit well below the purity levels needed to produce a weapon -- as long as its actions are proven to be peaceful and subject to airtight monitoring.
Israeli Prime Minister Benjamin Netanyahu, who has vehemently criticized the Geneva deal, has however called for a complete end to uranium enrichment in all its forms by Iran. Hawks on Capitol Hill in both political parties back his stance.
However, more pragmatic analysts in Washington argue that such a "perfect" deal is out of reach and would not be politically viable in Iran.
In the end, the key to a permanent deal may be some kind of diplomatic formula that allows the West to argue that Iran has made major concessions and rolled back its nuclear program to make the swift production of a weapon impossible and for Iranian negotiators to be able to proclaim to their domestic constituencies that they did not formally renounce the "right" to enrich uranium.
Several groups of Republican and Democratic senators are working to reconcile various different sanctions measures, believing that they would strengthen Obama's hand in negotiations.
Under the deal reached between world powers and Tehran to freeze Iran's nuclear program last month, Washington committed to "refrain from imposing new nuclear-related sanctions" for the six months during which world powers will seek to hammer out a comprehensive settlement.
Carney, however, would not say whether Obama would use his presidential veto to halt any congressional effort to impose new sanctions.