Barack Obama has revealed an exchange of letters with Iran's new President Hassan Rowhani but says his reluctance to strike Syria should not devalue US threats to thwart an Iranian nuclear bomb.
The US president, in an interview aired on Sunday, publicly confirmed the outreach to Rowhani for the first time, and said he believed the Syria chemical arms drama showed diplomacy could work if backed by threats of military action.
The exchange of letters will add to the notion the election of Rowhani offers a new possibility of a diplomatic way out of the showdown over Tehran's nuclear program.
But some analysts have questioned whether Obama's decision to hold off on military action against Syria will lead the Islamic Republic to conclude US threats against Tehran are empty.
In fact, Obama's top aides used a variation of that argument themselves, warning to members of Congress that blocking military action in Syria could send Iran the wrong message.
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But in his interview, Obama said the outcome of the Syrian deal offered Iran a "lesson" in the benefits of diplomacy.
Obama was asked on the ABC News This Week program whether he had reached out to Rowhani, a moderate conservative elected in June.
"I have. And he's reached out to me. We haven't spoken directly," Obama said.
The president was careful to draw a distinction between US behaviour over Syria - which ended in a deal with Russia to secure Damascus's chemical arms - and Washington's approach to Iran as a nuclear showdown reaches a critical point.
"I think what the Iranians understand is that the nuclear issue is a far larger issue for us than the chemical weapons issue," Obama said.
"The threat against ... Israel, that a nuclear Iran poses, is much closer to our core interests.
"A nuclear arms race in the region is something that would be profoundly destabilising.
"My suspicion is that the Iranians recognise they shouldn't draw a lesson - that we haven't struck (Syria) - to think we won't strike Iran."
Obama said on the other hand, the lesson from the showdown over Syria's chemical weapons, should show that "there is the potential of resolving these issues diplomatically".
Washington has repeatedly warned Iran that it has the option of military action, if diplomacy and crippling sanctions do not convince the Islamic Republic to stop short of building nuclear weapons.
Iran denies that its nuclear program has a military use.
