But her comments Thursday on the issue prompted him to question whether she has changed her mind.
During a Democratic presidential debate in July, Obama said he would be willing to meet without precondition in the first year of his presidency with the leaders of Iran, Syria, Venezuela, Cuba and North Korea.
Standing with him on stage, Clinton said she would first send envoys to test the waters and called Obama's position irresponsible and naive.
But asked about it Thursday by a voter, the New York senator said twice that she, too, would negotiate with Iran "with no conditions."
"I would engage in negotiations with Iran, with no conditions, because we don't really understand how Iran works. We think we do, from the outside, but I think that is misleading," she said at an apple orchard.
Obama's campaign wondered whether Clinton had changed her mind.
"Barack Obama will restore our place in the world by basing foreign policy decisions on consistent principles and not political calculation. That's a change we need and change we can believe in," said Leslie Miller, Obama's New Hampshire spokeswoman.
Clinton campaign spokesman Howard Wolfson later sought to clarify her comments, saying that while she believes in diplomatic engagement with Iran, "she does not agree with Senator Obama ... that the United States president should precommit to meeting directly with Mr. Ahmadinejad," the Iranian president.
Clinton on Thursday also characterized her recent vote to label Iran's Revolutionary Guard Corps a terrorist organization as a way to gain leverage for those negotiations.
Obama and other rivals for the Democratic presidential nomination in 2008 have been criticizing Clinton's vote late last month in favor of the resolution, comparing it to her 2002 vote authorizing the war in Iraq.
They have suggested that the Iran vote was the first step toward a military invasion there.
Austria does not intend to expel Russian diplomats because of the spy scandal