US president Barack Obama has said he hopes to have international sanctions against Iran in place "within weeks" because of its continuing nuclear programme.
Mr Obama said he and French president Nicolas Sarkozy, who is on a visit to the United States, are "inseparable" in their thinking on the subject.
But the US leader acknowledged he still lacks full support at the United Nations and said: "Do we have unanimity in the international community? Not yet. And that's something that we have to work on."
For his part, Mr Sarkozy told reporters Iran could not continue its "mad race" towards acquiring nuclear weapons, adding: "The time has come to take decisions."
Iran insists its nuclear programme is for civilian purposes, not nuclear weapons.
On the UN Security Council, veto-holding permanent members Russia and China have expressed reservations toward a tougher set of sanctions, as have several of the rotating members who do not have veto powers.
Mr Obama said he understands that countries that have business ties with Iran, especially those who depend on Iran for oil, might have reservations.
Still, Mr Obama said that, while "the door remains open if the Iranians choose to walk though it," there have been no signs that they are close to moving back from their nuclear programme, and patience has all but run out.
"My hope is that we are going to get this done this spring," he said. "So I'm not interested in waiting months for a sanctions regime to be in place. I'm interested in seeing that regime in place in weeks."
Earlier, after an international meeting of eight major powers in Quebec, US secretary of state Hillary Rodham Clinton predicted new sanctions would be forthcoming, hinting that sceptical nations such as China and Russia eventually would come along.