Supreme Leader Ayatollah Ali Khamenei's uncompromising demand for a halt to street protests over Iran's disputed presidential election puts him in the forefront of a power struggle that could turn bloody. In a rare Friday prayer sermon, Khamenei, 69, essentially read the riot act to anyone questioning the integrity of last week's election that gave hardline President Mahmoud Ahmadinejad a big margin over moderate challenger Mirhossein Mousavi. “If there is any bloodshed, leaders of the protests will be held directly responsible,” the black-turbaned, white-bearded cleric told tens of thousands of worshippers in Tehran in a televised speech that offered no concessions to the opposition. Iran, the world's fifth biggest oil exporter, whose nuclear program has alarmed the West, faces one of its gravest internal crises since the 1979 revolution. Iran expert Anoush Ehteshami of Durham University said Khamenei had made clear the gloves were coming off. “He was totally uncompromising and, dare I say, totally misreading the mood of the people in that he did not give an inch on their core demands,” Ehteshami said. Khamenei, whose authority theoretically cannot be challenged in Iran's complex system of clerical rule and limited democracy, appeared to offer his own life for the “Islamic revolution” in an emotional finale that drew tears from his audience. “We will do what we will have to do,” he declared. “I have an unworthy life, a defective body and little honour, which was given to me by you. I will put all of these on the palm of my hand and spend them on the path of the revolution and Islam.” The message of the Supreme Leader, whose right hand was crippled in a 1981 assassination attempt, was that defiance of his will amounted to a counter-revolutionary act, analysts said. Khamenei's proclaimed support for Ahmadinejad gives a stark choice to Mousavi's camp, which includes many pillars of Iran's clerical and political elite, such as former presidents Akbar Hashemi Rafsanjani and Mohammad Khatami: capitulate or face the full force of the security and judicial apparatus. There was no immediate word on how Mousavi, a former prime minister, and his influential backers would respond. Establishment insiders Ehteshami said he doubted such establishment insiders would defy Khamenei, who accused those asserting the election was rigged of playing into the hands of Iran's foreign enemies. “But if Mousavi stays the course, there will be violence,” Ehteshami predicted. “If the opposition feels there is no recourse through the legal due process, will they take up arms?” “We are really on a knife edge.” To enforce his writ, Khamenei can call on the elite Revolutionary Guard, the religious basij militia and other forces, but analysts said there would be a political cost. “All it does is put the Leader right in the middle of the fray,” said Iran analyst Ali Ansari of St Andrews University. “It will reassure his base, his core constituents, who will think it's the strong leadership they want, but those who are no longer convinced will be as disgusted as they were before. “For someone calling for national calm, he will have simply reinforced the polarities in the country,” Ansari added. Khamenei, chosen to succeed Iran's revolutionary founder, Ayatollah Khomeini, when he died in 1989, controls the armed forces and has the ultimate say in all matters of state, including nuclear policy and relations with the United States. But the drama of the past week, when hundreds of thousands of Iranians have ignored his calls for them to rally behind Ahmadinejad, accept the official election result and stay off the streets, may have dented his standing as the final arbiter. “Khamenei standing above the fray is out the window now. Whatever he does, he will have to take sides,” said Mehrdad Khonsari, an exiled Iranian opposition activist in London. Karim Sadjadpour, an associate at the Carnegie Endowment for International Peace, suggested that the power struggle sharpened by the election was taking Iran into uncharted territory. “Previously sacred red lines in Iran are now being challenged,” he wrote on the eve of Khamenei's address. “It is unprecedented that people would begin to openly challenge Khamenei's legitimacy as Supreme Leader, and indeed question the legitimacy of the institution of the Supreme Leader.” With his own authority at stake, Khamenei may feel compelled to suppress the most widespread anti-government protests Iran has witnessed since the revolution, even if it means confronting Mousavi's broad coalition of moderate and conservative leaders. “We are in for a long summer,” said Ansari. “The problem is that he will get short-term stability for long