US President Barack Obama has issued a stern defence of his outreach to Iran, warning politicians not to derail diplomatic efforts to curtail the Islamic state's nuclear program.
In an end-of-year news conference on Friday, Obama said efforts in Congress to pass tougher economic sanctions could damage recent moves to halt Tehran's alleged drive to refine nuclear fuel and build a weapon.
He underlined that any break in the diplomatic momentum towards a deal could force Washington into another military conflict.
Obama said the six-month interim agreement struck last month between Iran and world powers should stand as a test of Tehran's willingness to come to a deal.
"It is very important to test whether that's possible, not because it's guaranteed but because the alternative is us having to engage in some kind of conflict to resolve the problem with all kinds of unintended consequences," he said.
"It is my goal to prevent Iran from obtaining a nuclear weapon, but I sure would rather do it diplomatically."
The US and five other world powers - Britain, China, France, Germany and Russia - met Iranian envoys in Geneva last month and agreed on a six-month deal to reduce nuclear tensions.
Iran agreed to place its nuclear plants under UN watch, to halt new uranium enrichment and to dilute moderately enriched fuel stockpiles in exchange for a loosening of Western economic sanctions.
Iran insists it never intended to build a bomb, but its main regional foes Israel and Saudi Arabia, traditional US allies, want stronger action.
Some influential members of Congress, from Obama's Democratic Party and his Republican rivals, are pushing to pass laws that would tighten already strict US sanctions.
US Secretary of State John Kerry has warned this could torpedo the Geneva deal, and Obama himself took the opportunity on Friday to warn against any attempt to thwart the diplomatic track.
"We lose nothing during this negotiation period," he insisted. "There is no need for new sanctions legislation - not yet."
"Now, if Iran comes back and says, `we can't give you assurances that we're not going to weaponise' ... it's not going to be hard for us to turn the dials back, strengthen sanctions even further," he said.
On Thursday, 26 US senators introduced a bill to strengthen Iran sanctions, but the White House warned that Obama would veto the bill, meaning it would not become US law.
Iran last week reacted angrily when the US administration black-listed a dozen international firms for allegedly evading previous sanctions
