Obama made the comments to a small group of journalists at the White House after US officials rebuffed a call for a US-Iran summit.

The Washington Post said the president indicated international sanctions should remain in place on Tehran but that the regime should have a pathway for a peaceful settlement of the nuclear issue.

"It is very important to put before the Iranians a clear set of steps that we would consider sufficient to show that they are not pursuing nuclear weapons," Obama said, according to the Post.

"They should know what they can say 'yes' to."

The report said Obama left open the possibility that the United States would accept a deal that allows Iran to maintain its civilian nuclear program, so long as Tehran provides "confidence-building measures" to verify that it is not building a bomb.

An account of the meeting by The Atlantic magazine said Obama expressed the view that Iran is feeling the pain from sanctions but not yet changing their policies.

"It may be that their ideological commitment to nuclear weapons is such that they're not making a simple cost-benefit analysis on this issue," Obama was quoted as saying.

"Changing their calculus is very difficult, even though this is painful for them and we are beginning to see rumblings in Iran that they are surprised by how successful we've been."

On Tuesday, White House spokesman Robert Gibbs rebuffed a proposal from Iran's hardline President Mahmoud Ahmadinejad for face-to-face summit talks with Obama.

"We have always said that we'd be willing to sit down and discuss Iran's illicit nuclear program, if Iran is serious about doing that," Gibbs told reporters. "To date, that seriousness has not been there."

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