Without support from the United States and other Western countries, Iranian opposition groups will likely stop demonstrations against the Iranian regime and Mahmoud Ahmadinejad's declared victory in Friday's presidential elections, senior Israeli defense officials said Sunday. The officials speculated that the election results were likely due to "extreme fraud" by government officials. Ahmadinejad received over 60 percent of the vote, and former prime minister Mir Hossein Mousavi won just over 30%. "There was no way that the regime was going to let Mousavi win," explained one senior official. "The results clearly show that." According to the officials, a Mousavi victory would have been a blow to the regime, which is led by Supreme Leader Ayatollah Ali Khamenei, since the reformist candidate had called for changes to the implementation of Islamic law, particularly pertaining to the status of women in Iranian society. The officials also doubted whether the demonstrations that have rocked the streets of Teheran since Friday night would succeed in overturning the election results. "There have been mass arrests throughout Iran," another official explained, referring to the arrest of over 100 members of the reformist groups. "The regime fears the possibility of a revolution and will do everything it can to prevent that from happening." Among the arrested was Muhammad-Reza Khatami - brother of former president Muhammad Khatami and a former deputy speaker of parliament - as well as two top organizers of the country's largest reformist party, the Islamic Iran Participation Front: the party's secretary-general and the head of Mousavi's youth cyber campaign. Others were reportedly placed under house arrest and taken to undisclosed locations by security forces. Khatami and the two party activists were released Sunday. Mousavi on Sunday called on authorities to annul Friday's presidential election, saying it was the only way to restore public trust, as the angry protests continued in Iran in response to the election results. Mousavi, who claims to be the true winner of the election and has accused authorities of election fraud, urged his supporters to continue their "civil and lawful" opposition to results showing that Ahmadinejad won by a landslide. He advised police to stop violence against protesters. Mousavi's statement was posted Sunday on one of his campaign Web sites. Mousavi also met with Khamenei to discuss the fraud allegations. Shahab Tabatabaei, a prominent activist in Mousavi's pro-reform camp, said Mousavi had called on Khamenei to order the annulment of the election results. In Sunday's violence, protesters set fires and smashed store windows as groups challenging Ahmadinejad's reelection tried to keep pressure on authorities that have responded with anti-riot squads and blackouts of Web networks used to rally the pro-reform campaign. Ahmadinejad dismissed the unrest - the worst in Teheran in a decade - as "not important" and insisted that the election results were fair and legitimate. A huge rally in his support was organized even as clashes flared around the capital. There is little chance that the youth-driven Mousavi campaign could immediately threaten the pillars of power in Iran - the ruling clerics and the vast network of military and intelligence forces at their command - but it raises the possibility that a sustained and growing backlash could complicate Iran's policies at a pivotal time. US President Barack Obama has offered to open dialogue after a nearly 30-year diplomatic freeze. Iran also is under growing pressure to make concessions on its nuclear program or possibly face more international sanctions. In Paris, French Foreign Minister Bernard Kouchner said he was "very worried" about the crackdown on protesters. "France regrets that instead of openness, there has been quite a brutal response," he said. "This will leave its mark, and the opposition will organize itself." Scores of young people shouted "Death to the dictator!" on Sunday and broke the windows of city buses on several streets in central Teheran. They have burned banks, trash bins and piles of tires, using them as flaming barricades to block police. Riot police beat some of the protesters with batons, while dozens of others holding shields and motorcycles stood guard nearby. Shops, government offices and businesses closed early as tension mounted. Along Teheran's Vali Asr Street - where pro-Mousavi activists held a huge pre-election rally last week - tens of thousands of people marched in support of Ahmadinejad, waving Iranian flags and shouting his name. In a news conference, Ahmadinejad likened the violence to the intensity after a soccer match. "Some believed they would win, and then they got angry," he said. "It has no legal credibility. It is like the passions after a football match... The margin between my votes and the others is too much, and no one can question it." Ahmadinejad told a packed room of Iranian and foreign media that "in Iran, the election was a real and free one. The election will improve the nation's power and its future." He also accused foreign media of launching a "psychological war" against the country. Iranian authorities have asked some foreign journalists who were in Iran to cover the elections to prepare to leave. Nabil Khatib, executive news editor for Dubai-based news network Al-Arabiya, said the station's correspondent in Teheran had been given a verbal order Sunday from Iranian authorities that the office would be closed for one week. No reason was given for the order, but the station was warned several times Saturday that they needed to be careful in reporting "chaos" accurately. Iran restored cellphone service that had been down in the capital since Saturday. But Iranians could not send text messages from their phones, and the government increased its Internet filtering in an apparent attempt to undercut liberal voices. Social networking sites, including Facebook and Twitter, were also not working. The restrictions were likely intended to prevent Mousavi's supporters from organizing large-scale protests. But smaller groups assembled around the city. Some 300 Mousavi supporters gathered outside Sharif University, chanting, "Where are our votes?" About a dozen riot police used batons to disperse some 50 Mousavi supporters standing outside his campaign headquarters. On Saturday, the 67-year-old Mousavi released a Web message saying he would not "surrender to this manipulation." Teheran deputy prosecutor Mahmoud Slarkia told the semi-official ISNA news agency that fewer than 10 people had been arrested on the charge of "disturbing public opinion" through their "false reports" on Web sites after the election. He did not mention any names.