Won't let Iran get a nuclear weapon at any cost: Obama

United States President Barack Obama vowed to launch a new diplomatic push to solve the longstanding crisis over Iran's disputed nuclear programme but said he would not let Tehran acquire nuclear weapons at any cost.

"I very much want to see a diplomatic resolution to the problem. I was very clear before the campaign, I was clear during the campaign and I'm now clear after the campaign -- we are not going to let Iran get a nuclear weapon," Obama said.

"I think there is still a window of time for us to resolve this diplomatically. We've imposed the toughest sanctions in history. It is having an impact on Iran's economy," he said.

Obama said that there should be a way in which they can enjoy peaceful nuclear power while still meeting their international obligations and providing clear assurances to the international community that they're not pursuing a nuclear weapon.

"And so yes, I will try to make a push in the coming months to see if we can open up a dialogue between Iran and not just us but the international community, to see if we can get this thing resolved. I can't promise that Iran will walk through the door that they need to walk though, but that would be very much the preferable option," he said.

Obama refused to go into the details of negotiations.

"But I think it's fair to say that we want to get this resolved and we're not going to be constrained by diplomatic niceties or protocols. If Iran is serious about wanting to resolve this, they'll be in a position to resolve it," he said.

Outraged at the efforts of top Republican Senators on attacking US Ambassador to the UN Susan Rice on her comments on the Benghazi attack, Obama challenged the opposition lawmakers to go after him and not against one of the top American diplomat whom he is very proud of.

"If Senator (John) McCain and Senator (Lindsay) Graham, and others want to go after somebody? They should go after me. And I'm happy to have that discussion with them. But for them to go after the UN ambassador who had nothing to do with Benghazi? And was simply making a presentation based on intelligence that she had received? And to besmirch her reputation is outrageous," Obama said at a White House news conference.

"Let me say specifically about Susan Rice, she has done exemplary work. She has represented the United States and our interests in the United Nations with skill, and professionalism, and toughness, and grace. As I've said before, she made an appearance at the request of the White House in which she gave her best understanding of the intelligence that had been provided to her," he said.

Obama said he thinks it is important to find out exactly what happened in Benghazi.

"I'm happy to cooperate in any ways that Congress wants. We have provided every bit of information that we have and we will continue to provide information. And we've got a full-blown investigation, and all that information will be disgorged to Congress," he said.

On Syria, Obama said that his administration is not ready yet to recognise the Syrian opposition as has been done by France.

"We consider them a legitimate representative of the aspirations of the Syrian people. We're not yet prepared to recognize them as some sort of government in exile, but we do think that it is a broad-based representative group," Obama said responding to a question on Syria at a White House news conference.

"One of the questions that we're going to continue to press is, making sure that that opposition is committed to a democratic Syria, an inclusive Syria, a moderate Syria. We have seen extremist elements insinuate themselves into the opposition," he said.

"One of the things that we have to be on guard about, particularly when we start talking about arming opposition figures, is that we're not indirectly putting arms in the hands of folks who would do Americans harm, or do Israelis harm, or otherwise engage in actions that are detrimental to our national security," said the US President.