MOSCOW, June 15 (RIA Novosti) - Iran's Supreme Leader has ordered an inquiry into allegations by defeated presidential candidate Mir-Hossein Mousavi that the elections were rigged, the national television reported on Monday.

According to official election results, Iranian President Mahmoud Ahmadinejad was reelected on Friday, securing nearly 63% of the vote against former prime minister Mousavi's 34%. Mass protests by opposition supporters turned violent on Saturday and Sunday.

Mousavi on Saturday gave a written protest to the Guardian Council, effectively the country's highest legal body, and on Sunday met with the country's spiritual leader, Ayatollah Ali Khamenei, to discuss the letter.

"Naturally in this election, complaints should be followed through legal channels," Khamenei was quoted as saying on national television, adding that it was necessary to "pursue the issue calmly."

He told Mousavi he had instructed the Guardian Council to closely examine the letter.

Khamenei had said on Saturday that the election had been conducted fairly, and urged Iranians to accept the results.

Ahmadinejad dismissed on Sunday allegations of election fraud, and called his victory a blow to the "oppressive system" ruling the world.

Thousands of Mousavi's supporters gathered on the streets of Tehran on Saturday, protesting against alleged ballot fraud. By evening the demonstrations had turned violent, with rioters burning police motorcycles and smashing shop windows. Police fought back the protesters with batons and tear gas. According to protesters, several dozen people were arrested.

Ahmadinejad called Saturday's vote free and fair, and said: "The margin between my votes and the others' is too much and no one can question it... The election will improve the nation's power and its future."

Mousavi, however, vowed to pursue his claims of fraud.

"I personally strongly protest against the many obvious violations, and I warn that I will not surrender to this dangerous charade," the former premier said in a statement. "People who stood in long lines and knew very well who they were voting for were utterly astonished by the magicians working at the television and radio stations."

"This result will jeopardize the pillars of the Islamic Republic and establish tyranny," he said.

Independent election observers were banned from polling stations, and several countries have voiced alarm over the post-election violence.