Obama Raises Specter Of War With Iran If Congress Imposes New Sanctions

"We have shown that we are credibly trying to solve this problem and avert some sort of military showdown. In that context, there is no good argument for us to - undercut - undermine, the negotiations," Obama said.

The White House and Iran are currently locked in negotiations for Iran to roll back its nuclear program in exchange for the US and others lifting their sanctions against the Iranian government. These negotiations have been repeatedly extended and frustrated members of Congress said they fear Obama will not strike a tough enough deal. Even Democrats have backed legislation to strengthen the sanctions against Iran.

Speaking at a joint press conference with British Prime Minister David Cameron, Obama said such legislation would likely result in the negotiations collapsing. He argued Iran could easily return to building a military-grade nuclear reactor - setting the stage for an aggressive showdown.

"They would be able to maintain that the reason that they ended negotiations was because the United States was operating in bad faith and blew up the deal," he said. "The likelihood [that] the entire negotiations collapses is very high. And if that happens, there is no constraint on Iran at that point going back and doing exactly what it had been doing before: ... developing a heavy water reactor, that once built is extraordinarily difficult to dismantle."

Obama also argued that, should federal lawmakers pass tough new anti-Iran legislation, they will "own" any violent fallout from the negotiations' collapse. He hinted the American public may then hold congressional members responsible for the failure.

"Congress should be aware that if this diplomatic solution fails, then the risks and likelihood that this ends up being at some point being a military confrontation is heightened. And Congress will have to own that as well," he said.

He further vowed to veto any new Iran sanctions that reach his desk.

"Congress needs to show patience," he said. "I will veto a bill that comes to my desk. And I will make this argument to the American people as to why I am doing so. And I respectfully request them to hold off for a few months to see if we have the possibility of solving a big problem without resorting, potentially, to war."