WASHINGTON, June 15 (Xinhua) -- The United States is "deeply troubled" by the growing rioting which has flared in Iran because of the disputed presidential elections, State Department spokesman Ian Kelly said here on Monday.

    "Along with the rest of the international community ... we are deeply troubled by the reports of violent arrests and possible voting irregularities," Kelly told reporters.

    Some 39 million out of 46.2 million eligible Iranian voters cast their ballots on Friday to elect a new president of the Islamic Republic.

    It was reported that angry demonstrators clashed with police in Tehran, the capital of Iran, since the weekend after Iranian authorities declared incumbent President Mahmoud Ahmadinejad the winner of the presidential ballot.

    Former Iranian Prime Minister Mir Hossein Mousavi, who was Ahmadinejad's main rival in the presidential campaign, has denounced the balloting as a fraud and has called for the cancellation of the results.

    Mousavi said at a banned rally in Tehran on Monday that he was ready to take part in a new election.

    To curb escalating national turmoil, Iran's Supreme Leader Ayatollah Ali Khamenei has ordered the Guardian Council of the Constitution, which enjoys the right for acceptance or rejection of elections' legality and candidates' competency, to investigate the claims of fraud in the recent presidential election.

    Both the White House and the State Department have refrained from making direct comment on the re-election of Iranian incumbent President Mahmoud Ahmadinejad. Instead, it said it would continue to monitor the political development in the Islamic Republic.