Obama on Thursday pressed Congress as the UN nuclear agency said that Iran has not expanded its nuclear facilities in the past three months in a possible confidence-building measure by the new reform-minded government.
Obama appeared to make his most explicit suggestion yet that military action -- if diplomacy fails -- would have dangerous effects and only fuel an Iranian desire for nuclear weapons.
"What we have done is seen the possibility of an agreement in which Iran would halt advances on its program," Obama told a news conference as Iran, the United States and other powers prepare next week for their third round of talks since October.
"We can buy some additional months in terms of their breakout capacity. Let's test how willing they are to actually resolve this diplomatically and peacefully," he said.
Obama said that his intention "always was to bring the Iranians to the table so we could resolve this issue peacefully."
"No matter how good our military is, military options are always messy, are always difficult, always have unintended consequences, and in this situation are never complete in terms of making us certain that they don't then go out and pursue even more vigorously nuclear weapons in the future," he said.
"If we're serious about pursuing diplomacy, there's no need for us to add new sanctions on top of the sanctions that are already very effective and that brought them to the table in the first place," Obama said.
Secretary of State John Kerry, revealing the details of the US offer to Iran for the first time, said that "95 percent or more" of sanctions would be in place but that Iran would gain access to a small portion of assets.
Iran had been earning $110-120 billion a year from oil sales, but the figure was cut down to $40-45 billion -- and remains frozen in banks around the world -- due to the US-led sanctions campaign, Kerry said.
"All we are talking about doing is a tiny portion of that would be released because you have to do something to make it worth while for them to say yes, we are going to lock our program where it is today and actually roll it back," Kerry told MSNBC television in an interview.
In Vienna, the International Atomic Energy Agency said that Iran in the last three months has installed only four new centrifuges at its Natanz plant, compared with 1,861 machines put in place in the previous period.
And at the Fordo facility, which also enriches uranium no new centrifuges were put into operation, according to the quarterly report.
It added that Iran has also not begun operating any new-generation IR-2M centrifuges and that no "major components" had been installed at a reactor being built at Arak.
The report is the first since President Hassan Rouhani took office. In September, he spoke by telephone to Obama in the first contact between the two nations' leaders since the 1979 Islamic Revolution overthrew the pro-Western shah.
The US Congress is discussing even tighter sanctions on Iran's oil program by removing exemptions for nations that still buy the country's oil.
Senator Mark Kirk, a leader of the sanctions push, said after talks with Kerry that a moderate in Tehran is "an Iranian who is out of bullets and out of money."
Iranian hardliners have also attacked Rouhani's outreach, with some arguing that the United States will always be hostile.
In a sign of hope for a deal, Kerry and other foreign ministers flew last week to Geneva for the talks between Iran, the United States and five other powers -- Britain, China, France, Germany and Russia.
Kerry is not scheduled to attend the upcoming round next week in Geneva but is keeping the option open, State Department spokeswoman Jen Psaki said.
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