Iran's supreme leader sought to end the deepening crisis over disputed elections with one decisive speech - declaring the vote will almost certainly stand and sternly warning opposition leaders to end street protests or be held responsible for any "bloodshed and chaos" to come. But a first sign of possible resistance came shortly after nightfall in Teheran Friday. Cries of "Death to the dictator!" and "Allahu akbar" - "God is great" - rang from rooftops in what's become a nightly ritual of opposition unity. The sharp line drawn by Iran's most powerful figure, Ayatollah Ali Khamenei, is a gambit that pushes Iran's opposition to a pivotal moment: either back down or risk a crushing response from police and the forces at Khamenei's disposal - the powerful Revolutionary Guard and their volunteer citizen militia, the Basij. It also presents important tests for opposition leader Mir Hossein Mousavi. He now must examine his willingness to challenge the Islamic leadership he once served as prime minister. There are further questions about his ability to control his own followers, who are waiting for a clear response to Khamenei's edict before a rally planned for Saturday. Since the June 12 election, Mousavi has become the figurehead for a broad collection of demonstrators - from the most liberal-leaning reformists to religious conservatives - brought together by claims that fraud was behind the landslide re-election of President Mahmoud Ahmadinejad. Some could be prepared to take their protests to the limit. Many others, however, have no interest in an all-out mutiny against the country's Islamic system and know authorities have the tools to strike back without mercy. Khamenei was blunt about what a wider fight would bring - warning those who "want to ignore the law or break the law" will face the consequences. "They will be held accountable for all the violence, bloodshed and rioting," he told tens of thousands of people gathered for Friday prayers at Teheran University for a speech that was broadcast around Iran and the world. Police clashed with protesters in running battles around Teheran immediately after the election and the Basij militia had a reported role in attacks at the university. Gunfire from a Basij compound in Teheran also left at least seven people dead Monday. Khamenei even offered muted criticism of security forces, saying he objected to "misconducts" such as attacks on students. But the full force of the police and Revolutionary Guard has remained in check. And this was Khamenei's implicit message since the Guard and the vast volunteer militia force it controls is under direct command of the ruling clerics. As he concluded his sermon, Khamenei invoked the names of Shiite saints and began weeping. Among the worshippers sitting on the carpeted floor of the mammoth prayer hall was Ahmadinejad in a tan jacket and one of his three election rivals, former Revolutionary Guard commander Mohsen Rezaei. Crowds spilled into the campus. Mousavi and candidate Mahdi Karroubi, the only cleric in the race, were not shown on state TV coverage and apparently did not attend. Iranian authorities have placed strict limits on the ability of foreign media to cover recent events, banning reporting from the street and allowing only phone interviews and information from officials sources such as state TV. "The Islamic state would not cheat and would not betray the vote of the people," said Khamenei, standing on a raised platform decorated with Quranic verses and flanked by flowers. He went on to effectively declare Ahmadinejad the winner, calling the election an "absolute victory." He left open a remote chance that the overall outcome could come under question by the Guardian Council, an unelected body of 12 clerics and Islamic law experts close to the supreme leader. The council investigates voter fraud claims. The council has said it was prepared to conduct a limited recount of ballots at sites where candidates claim irregularities. It not clear, however, if they have initiated any probes. A spokesman for Mousavi said Friday the opposition leader is not under arrest but is not allowed to speak to journalists or stand at a microphone at rallies. Iranian filmmaker Mohsen Makhmalbaf told the AP from Paris it's even becoming difficult to reach people close to Mousavi. He said he has not heard from Mousavi's camp since Khamenei's address. Mousavi has showed backbone in pressing his claims of election irregularities. But he would be an unlikely rebel against the entire state. His roots in the Islamic leadership date to the early years after the 1979 Islamic Revolution. He served as prime minister in the 1980s when Khamenei was president - a point the supreme leader made in his address. The anger over the alleged vote-rigging "has coalesced behind Mousavi," said Michael Hanna, a Middle East analyst based in New York. "But all the main protagonists are figures from within the establishment of the Islamic Republic," he said. "It doubtful whether Mousavi (and his political backers) are really out to overturn the basic structures and underpinnings of the Islamic Republic." The protest movement, however, has appeared to gain some solid footing after days of street clashes that left parts of Teheran scorched and battered. Four consecutive days of huge marches this week streamed through Teheran with powerful images. Mousavi urged supporters to wear black in mourning for the alleged vote-rigging and those who died in the violence. "Some people assume that through street riots they can have pressure over the establishment, and try to force the officials to actually listen to them. This is also wrong," Khamenei said. He also accused foreign media and Western countries of trying to create a political rift and stir up chaos. Iranian leaders often blame foreign "enemies" for plots against the country, but Khamenei's comments suggest Iran could remain cool to expanding dialogue with the West and the offer of opening talks with Washington. Khamenei blamed the United States, Britain and "other enemies" for fomenting unrest. British Prime Minister Gordon Brown and other European Union leaders expressed dismay over the threat of a crackdown. The British Foreign Office told Iran's charge d'affairs in London that Khamenei's comments were "unacceptable and had no basis in fact," a spokesman said on condition of anonymity in line with policy. Both houses of the US Congress approved a resolution condemning "the ongoing violence" by the Iranian government and its suppression of the Internet and cell phones. The Republican-backed resolution was a veiled criticism of President Barack Obama, who has been reluctant to speak too strongly about the disputed election. In an interview taped Friday with CBS, Obama said he is very concerned by the "tenor and tone" of Khamenei's comments. He also said that how Iran's leaders "approach and deal with people who are, through peaceful means, trying to be heard" will signal "what Iran is and is not." In Switzerland, Iranian Nobel Peace laureate Shirin Ebadi said Iran should hold a new election observed by international monitors, adding that more than 500 people have been arrested since the balloting. The crowds in Teheran and elsewhere have been able to organize despite a government clampdown on the Internet and cell phones. The government has blocked certain Web sites, such as BBC Farsi, Facebook, Twitter and several pro-Mousavi sites that are conduits for Iranians to tell the world about protests and violence. Text messaging has not been working in Iran since last week, and cell phone service in Teheran is frequently down.