WASHINGTON: US President Barack Obama said on Tuesday that there was no need to decide now on military action against Iran and said new talks would show “quickly” how serious Tehran is about resolving the nuclear standoff.

“Iran is feeling the bite of these sanctions in a substantial way. The world is unified, Iran is politically isolated. And what I have said is that we will not countenance Iran getting a nuclear weapon,” Obama told reporters at a White House press conference.

“We're now seeing noises about them returning to the negotiating table, that it is deeply in everybody's interests, the United States', Israel's, and the world's, to see if this can be resolved in a peaceful fashion.

“And so this notion that somehow we have a choice to make in the next week or two weeks or month or two months is not borne out by the facts.” Israeli Prime Minister Benjamin Netanyahu warned during a US visit on Monday that it could not afford to wait “much longer” for sanctions to work, and said he would “never let my people live in the shadow of annihilation”.

Obama lashed out at criticism from Republican rivals over his Iran policy, saying “bluster” is not helping resolve the crisis and accusing them of repeating the same policies he has been pursuing for three years.

“This is not a game, and there's nothing casual about it,” the president said. “When I see the casualness with which some of these folks talk about war, I'm reminded of the costs involved in war.” Republican frontrunner Mitt Romney suggested he would be more willing than Obama to consider using military force while his main rival for the presidential nomination Rick Santorum backed an ultimatum demanding Iran stop nuclear production or face action by the US to “tear down” its facilities.

In Brussels, EU foreign policy chief Catherine Ashton, speaking on behalf of Britain, China, France, Germany, Russia and the United States, reiterated an offer to resume talks with Tehran.

The Obama administration has said it does not believe Iran has taken a decision to develop a nuclear weapon, or that the time is right for military action, preferring to give biting new sanctions time to work.

However Israel, which sees a possible Iranian nuclear weapon as a threat to its existence, believes that Iran may be on the cusp of “break out” capability -- the moment when it could quickly build a nuclear weapon.