Iran''s newly re-elected president, Mahmoud Ahmadinejad, dismissed on Sunday allegations of election fraud, and called his victory a blow to the "oppressive system" ruling the world.

Tehran has been hit by a second day of protests over the election, which the incumbent leader won with 63% of votes. The reformist challenger Mir Hossein Mousavi, who was widely expected to either win or force a second voting round, garnered only 34%.

Speaking at his first news conference after his victory, Ahmadinejad said: "The fact that some are protesting and questioning the results is natural. They thought they would win, and were preparing for this, so it makes them upset."

He 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."

He cited the record high turnout of 84% as a blow to countries that oppose Iran.

On Iran''s nuclear power program, which many countries suspect is a cover for a weapons program, the president said nuclear development would continue, and that the international dispute is "a thing of the past."

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.

Smaller-scale riots continued on Sunday.

Mousavi earlier said he would refuse to recognize Ahmadinejad''s victory.