Editor's note: Iranian authorities have barred journalists for international news organizations from reporting on the streets and ordered them to stay in their offices. This report is based on the accounts of witnesses reached in Iran and official statements carried on Iranian media.

Iran's increasingly isolated opposition leader effectively ended his role in street protests, saying he'll seek permits for future rallies. A senior cleric demanded in a nationally broadcast sermon Friday that leaders of the unrest be punished harshly and that some are "worthy of execution."

Iran's ruling clergy has widened its crackdown on the opposition since a bitterly disputed June 12 presidential election, and scattered protests have replaced the initial mass rallies.

The official Web site of opposition leader Mir Hossein Mousavi, 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 hard-line President Mahmoud Ahmadinejad as the winner.

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.

Hundreds have been detained since the vote, including journalists, academics and university students, and a special court has been set up to put them on trial.

President Barack Obama, joined at the White House by German Chancellor Angela Merkel, hailed the demonstrators in Iran and condemned the violence against them.

"Their bravery in the face of brutality is a testament to their enduring pursuit of justice," Obama said. "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 brushed aside accusations Thursday of U.S. meddling in Iran by Ahmadinejad, who called for "repentance" by the U.S. leader. Obama added that Mousavi has "captured the imagination or spirit" of those inside Iran who are "interested in opening up."

In a Friday sermon at Tehran 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 alleged that some involved in the unrest had used firearms.