Sharpening tone, White House condemns Iran violence

* US concerned that Iran recognize 'world is watching'

* McCain says election was 'corrupt'

* White House supports congressional resolutions

By Jeff Mason and Steve Holland

WASHINGTON, June 19 (Reuters) - President Barack Obama toughened his rhetoric on Friday in support of Iranian demonstrators protesting a disputed presidential election and criticized the Tehran government for its violent response.

Obama's comments came after a strong warning to protest leaders by Iran's supreme leader and criticism by Republican lawmakers, led by Senator John McCain, of a tepid White House response to the protests and to charges the vote was rigged.

"I'm very concerned based on some of the tenor -- and tone of the statements that have been made -- that the government of Iran recognize that the world is watching," Obama told CBS News.

"And 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 -- and is not."

Iranian Supreme Leader Ayatollah Ali Khamenei said on Friday that last week's election was won fairly by President Mahmoud Ahmadinejad and not rigged, as defeated candidate Mirhossein Mousavi alleges. Khamenei warned protest leaders they would be responsible for any bloodshed.