Washington - US President Barack Obama said he was concerned by Iranian supreme leader Ayatollah Ali Khamenei's speech Friday that called for an end to protests over Iran's disputed election and suggested a government crackdown could be coming.

"I'm very concerned based on some of the tenor and tone of the statements that have been made," Obama said in an interview with CBS News. Iran should "recognize that the world is watching."

"How they approach and deal with people who are, through peaceful means, trying to be heard will, I think, send a pretty clear signal to the international community about what Iran is ... and is not," Obama said.

Khamenei threw his weight behind re-elected President Mahmoud Ahmadinejad, insisting no fraud had taken place in the June 12 election.

He also issued a stern warning that illegal demonstrations were not acceptable, and that the opposition would be held responsible for any outbreaks of violence. Hundreds of thousands of people have been protesting in support of opposition candidate Mir-Hossein Moussavi.(dpa)