WASHINGTON  - The White House has 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.

Meanwhile, the accord with Iran to curb its nuclear programme means a planned NATO anti-missile system in Europe, hotly opposed by Moscow, is no longer necessary, Russian Foreign Minister Sergei Lavarov argued Wednesday.

Moscow fears the system would compromise its own defences while NATO says the project is meant only to protect Europe from Iranian development of long-range missiles. The prospect that Iran would also develop a nuclear weapon -- strongly rejected in Tehran -- added to the momentum for the NATO defence system.

Now, if the agreement with Iran "is fully implemented... then there will no reasons to create a missile defence system in Europe," Lavrov said. Lavrov reiterated that, for Russia, the system is a major problem in relations with NATO, the military alliance set up by Washington to counter the Soviet Union in the Cold War.

Last month, the five permanent members of the UN Security Council -- Britain, China, France, Russia and the United States -- plus Germany agreed an accord with Iran to curb its nuclear programme in return for an easing of sanctions.

The initial deal is supposed to lead to a comprehensive accord which would bring Iran's nuclear programme back under full international oversight to ensure it is a civilian not military project, with crippling sanctions progressively lifted.