The violence perpetrated against Iranian demonstrators "is outrageous," US President Barack Obama said Friday. "Their bravery in the face of brutality is a testament to their enduring pursuit of justice," Obama said at the White House, where he was joined by German Chancellor Angela Merkel. "The violence perpetrated against them is outrageous. In spite of the government's efforts to keep the world from bearing witness to that violence, we see it and we condemn it." Obama scoffed at accusations Thursday of US meddling in Iran by Ahmadinejad, who called for "repentance" by the US leader. Obama added that opposition leader Mir Hossein Mousavi had "captured the imagination or spirit" of those inside Iran who are "interested in opening up." Iran's increasingly isolated opposition leader effectively ended his role in street protests, saying he'd seek permits for future rallies. A leading cleric demanded in a nationally broadcast sermon Friday that leaders of the unrest be punished harshly and said some are "worthy of execution." Iran's ruling clergy has widened its clampdown on the opposition since a bitterly disputed June 12 presidential election, and scattered protests have replaced the initial mass rallies. Mousavi's official Web site, his main tool of communicating with his supporters, was hacked Friday, leaving it blank, an aide said. Mousavi has said victory was stolen from him through fraud, challenging the proclamation of President Mahmoud Ahmadinejad as the winner. However, Mousavi has sent mixed signals to his supporters in recent days, asking them not to break the law, while pledging not to drop his challenge of the election results. On Thursday, Mousavi said for the first time that he was being isolated by authorities and pressured to drop his presidential election challenge, while Ahmadinejad, sharply criticized Obama. In another sign of the widening post-election crackdown, 70 university professors were arrested late Wednesday, after a meeting with Mousavi. The detention of the professors signaled that the authorities are increasingly targeting Iran's elite. Hundreds of protesters and activists are believed to have been taken into custody since the June 12 vote, including journalists, academics and university students, and a special court has been set up to try them. Ahmadinejad dismissed growing Western criticism of the post-election clampdown, singling out the US president. "Why has Mr. Obama, who advocates change, been trapped and follows the same path as Bush?" state TV quoted Ahmadinejad as saying. In Friday's central Muslim sermon at Teheran University, a senior cleric, Ayatollah Ahmed Khatami, called for harsh retribution for dissent. "Anybody who fights against the Islamic system or the leader of Islamic society, fight him until complete destruction," he said in the nationally broadcast speech. The cleric claimed some involved in the unrest used firearms. "Anyone who takes up arms to fight with the people, they are worthy of execution," he said. "We ask that the judiciary confront the leaders of the protests, leaders of the violations, and those who are supported by the United States and Israel strongly, and without mercy to provide a lesson for all." Khatami said those who disturbed the peace and destroyed public property were "at war with God," and said they should be "dealt with without mercy." He reminded worshipers that Iran's supreme leader, Ayatollah Ali Khamenei, rules by God's design and must not be defied. The cleric also lashed out at foreign journalists, accusing them of false reporting, and singled out Britain for new criticism. "In this unrest, Britons have behaved very mischievously and it is fair to add the slogan of down with England to slogan of down with USA," he said, as his remarks were interrupted by worshipers' chants of "Death to Israel." Iran's rulers have accused the West, which has become increasingly vocal in its condemnation of the post-election clampdown, of meddling in Iran's internal affairs. Earlier this week, Iran expelled two British diplomats, prompting the expulsion of two Iranian diplomats by Britain. In Trieste, Italy, foreign ministers of the Group of Eight countries called for an end to the violence in Iran and urged the authorities to find a peaceful solution. Khatami, meanwhile, alleged that the icon of the opposition, slain protester Neda Agha Soltan, was killed by demonstrators, not the Iranian security forces. Soltan, 27, was killed by a shot to the chest last week, on the sidelines of a protest. "The proof and evidence shows that they (protesters) have done it themselves and have raised propaganda against the system," he said. "I say hereby that these deceitful media have to know that the ordeal will be over and shame will remain for them." In London, Dr. Arash Hejazi, who said he tried to save Soltan as the young woman bled to death, told the BBC she apparently was shot by a member of the Basij militia. Protesters who spotted an armed member of the Basij militia on a motorcycle, stopped and disarmed him, the doctor said. The man appeared to admit shooting Soltan, shouting "I didn't want to kill her," but the furious protesters confiscated his identity card and took photographs of him before letting him go, Hejazi said. In quelling protests, Basij militiamen have broken up even small groups of people walking together to prevent any possible gathering. Still, dozens of friends and relatives of Soltan managed to pay tribute Friday, arriving at Teheran's Behesht-e Zahra cemetery in groups of two and three, uttering brief prayers, placing flowers on Soltan's grave and then leaving, witnesses said. Vigils for Soltan have been held around the world. Khamenei has ordered a large security detail around Mousavi - ostensibly to protect him, but presumably also to restrict his movements. Authorities have also targeted those close to Mousavi. Late Thursday, state TV reported that the head of Mousavi's information committee, Abolfazl Fateh, was banned from leaving Iran for Britain. The report, which could not be verified independently, identified Fateh as a doctoral student in Britain. The semiofficial Fars news agency said Fateh was banned from travel so authorities could investigate "some of the recent gatherings," a reference to election protests. At least 11 Mousavi campaign workers and 25 staffers on his newspaper have been detained since the election. In all, at least 17 people have been killed in post-election protests, in addition to eight members of the Basij, the government has said.