Iran ? Iran’s embattled opposition leader vowed Thursday that he wouldn’t back down from challenging what he called a rigged presidential election despite the regime’s increasing attempts to isolate him, telling the hard-liners: “I won’t leave the picture.”

Incumbent President Mahmoud Ahmadinejad, proclaimed the landslide winner of the balloting, accused President Barack Obama of meddling in Iran’s affairs. “Correct yourself,” he told the U.S. leader, urging him to “show your repentance.”

On his Web site, opposition leader Mir Hossein Mousavi leveled unusually strong criticism at the Islamic regime’s leaders, saying they were “the main factor for the recent violence and unrest and have spilled the blood of the people.” His allegation came nearly a week after supreme leader Ayatollah Ali Khamenei warned the opposition to end street protests or be held responsible for any “bloodshed and chaos.”

Khamenei has refused to order a new vote despite the biggest demonstrations in the country since the 1979 Islamic Revolution.

“I am not ready to withdraw from demanding the rights of the Iranian people,” Mousavi said, adding that he was determined to prove electoral fraud.