The White House on Wednesday shrugged off complaints from Iran that the United States was meddling in its affairs. Spokesman Robert Gibbs said that US President Barack Obama had struck the right tone in commenting about Iran's presidential election dispute in Iran. The Iranian government had reportedly summoned the Swiss ambassador, who represents US interests in Iran, to complain about American interference. Gibbs said Obama has been clear that there is "a vigorous debate in Iran, between Iranians, about their leadership." Gibbs said Obama stands by his defense of principles such as the right of people to demonstrate in peace. Alleging for the first time that Washington had fueled the bitter post-election dispute, Iran had accused the US of "intolerable" meddling in its internal affairs. Meanwhile, opposition supporters marched in huge numbers through Teheran's streets for a third straight day to protest the outcome of the balloting. 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 Teheran in support of pro-reform, a demonstration that swallowed several lanes of traffic and appeared to stretch for many blocks. Marchers flashed the victory sign or carried placards, and some were dressed in green - the color of Mousavi's campaign. It was the third day in a row that Mousavi supporters have taken to the streets, and he called for another demonstrations on Thursday - a direct challenge to Supreme Leader Ayatollah Ali Khamenei and the cleric-led system. Mousavi is calling for the election to be declared invalid and held again. Khamenei has told Mousavi to pursue his demands through the electoral system and called for Iranians to unite behind their Islamic government, an extraordinary appeal in response to tensions over the vote. Mousavi still called for his followers to wear or carry black in mourning Thursday for the alleged election fraud and the deaths of protesters. Official media have reported seven deaths. The street protests, paired with dissent from powerful clerical and political figures, have presented one of the gravest threats to Iran's complex blend of democracy and religious authority since the system emerged from the 1979 Islamic Revolution. Several Iranian soccer players wore green wrist bands Wednesday during a World Cup qualifying match in South Korea that was televised in Iran. Blogs and Web sites such as Facebook and Twitter have become vital conduits for Iranians to inform the world about protests and violence. The BBC said the jamming of its broadcasts had become "progressively worse," with its BBC Arabic television and other language services knocked off the air at various points by interference traced to Iran. A spokeswoman said traffic for both the Voice of America's Persian language service and Radio Farda sites had increased by 200 percent since before the election but radio and for television jamming persisted. Videos and photos posted by people inside Iran show scenes of violence that have not been reported through official channels. The new media restrictions make it virtually impossible to independently verify much of the information, which includes dramatic images of street clashes and wounded demonstrators. Much of the imagery has been posted anonymously. In other cases, those who have posted have declined to be identified due to fear of government retaliation, or cannot be reached due to government restrictions on the Internet and mobile phones. One such image, purportedly from the southern city of Shiraz, showed crowds walking in the street around a burning motorcycle that some say belonged to pro-government militia members who attacked protesters. Mousavi and reformist former President Mohammad Khatamiwrote a letter to the State Security Council, the country's highest authority on internal security, to complain about attacks on protesters by plainclothes "basiji," a paramilitary force under the Revolutionary Guard. Mousavi said militiamen had been smashing windows, setting cars on fire and attacking people with batons, iron chains and bars and authorities had been blaming Mousavi supporters. He also wrote to the head of the judiciary to complain about attacks on protesters and arrests of activists from their homes. The Revolutionary Guard, an elite military force answering to Khamenei, said through the state news service that its investigators have taken action against "deviant news sites" that encouraged public disturbances. The Guard is a separate military with enormous domestic influence and control of Iran's most important defense programs. It is one of the key sources of power for the ruling establishment. The statement alleged that dissident Web sites were backed by Canadian, US and British interests. "Legal action will be very strong," it said. Unlike many dissidents, Mousavi has the ability to press his case with Iran's highest authorities and could gain powerful allies. Some influential clerics have expressed concern about possible election irregularities, and a fierce critic of Ahmadinejad, former President Hashemi Rafsanjani, is part of the ruling establishment. Iranian TV showed pictures of Faezeh Hashemi, Rafsanjani's daughter, speaking to hundreds of Mousavi supporters, carrying pictures of Khomeini and others. Iran's most senior dissident cleric, Grand Ayatollah Hossein Ali Montazeri, said widespread vote fraud had undermined the legitimacy of the ruling Islamic system and that "no sound mind" would accept the results. "A government that is based on intervening in (people's) vote has no political or religious legitimacy," said Montazeri, who had once been set to succeed Ayatollah Ruhollah Khomeini as supreme leader until he was ousted because of criticisms of the revolution. State media said Khamenei would deliver the sermon at Friday prayers, the most important religious address of the week. The supreme leader generally leads Friday prayers only two or three times a year. The US-based International Campaign for Human Rights in Iran said several dozen noted figures associated with the reform movement have been arrested, among them politicians, intellectuals, activists and journalists. Analyst Saeed Leilaz, who is often quoted by Western media, was arrested Wednesday by plainclothes security officers at his home, said his wife, Sepehrnaz Panahi. The group said Mohammad-Reza Jalaipour, another noted Iranian analyst, had also been arrested. At least 10 Iranian journalists have been arrested since the election, Reporters Without Borders said, and a Web site run by former Vice President Mohammad Ali Abtahi said the reformist had been arrested. Prominent reformer Saeed Hajjarian has also been detained, Hajjarian's wife, Vajiheh Masousi, told The Associated Press. Hajjarian is a close aide to former President Mohammad Khatami. The main electoral authority has said it was prepared to conduct a limited recount of ballots at sites where candidates claim irregularities. The recount would be overseen by the Guardian Council, an unelected body of 12 clerics and Islamic law experts close to Khamenei. But Mousavi alleges the Guardian Council is not neutral and has already indicated it supports Ahmadinejad. Ahmadinejad, who has dismissed the unrest as little more than "passions after a soccer match," attended a summit Tuesday in Russia that was delayed a day by the unrest. He returned to Iran and held a cabinet meeting, saying on state television Wednesday that people had voted for his "policies of justice."