Opposition supporters marched in huge numbers through Tehran's streets for a third straight day to protest the outcome of the balloting.

The Iranian government summoned the Swiss ambassador, who represents US interests in Iran, to complain about American interference, state-run Press TV reported.

The English-language channel said the government called Western interference 'intolerable.' A State Department spokesman said the US was withholding judgment about the election and not interfering in Iranian internal affairs.

President Barack Obama has reacted cautiously to opposition allegations that President Mahmoud Ahmadinejad stole the election, saying he shared the world's 'deep concerns' but it was 'not productive, given the history of US-Iranian relations, to be seen as meddling.'

The two countries broke off diplomatic relations after the 1979 Islamic Revolution and Iranian hard-liners frequently accuse internal enemies of allying with the US and other Western powers to overthrow the ruling system.

Iran summoned the Czech, France, German and British ambassadors Tuesday, state television said.

A crackdown on dissent continued, with more arrests of opposition figures reported, and the country's most powerful military force - the Revolutionary Guard - saying that Iranian Web sites and bloggers must remove any materials that 'create tension' or face legal action.

But supporters were undeterred in their support of reformist candidate Mir Hossein Mousavi, who has called himself the winner of the June 12 election.

Amateur video and state television footage showed thousands of people marching along an overpass in Tehran in support of pro-reform, a demonstration that swallowed several lanes of traffic and appeared to stretch for many blocks. -- AP