Iran's opposition leader received another stern warning Saturday not to encourage his supporters to take to the streets a day after the country's top leader sought to end the deepening election crisis by effectively declaring President Mahmoud Ahmadinejad the winner.

Supporters of opposition leader Mir Hossein Mousavi have planned a massive rally in Tehran later Saturday, but it was unclear if he would attend and how large the rally would be after Supreme Leader Ayatollah Ali Khamenei ordered opposition leaders on Friday to end street protests or be held responsible for any "bloodshed and chaos" to come.

A top Iran police official, Ahmad Reza Radan, warned Mousavi Saturday that if people take to the streets, "their leaders will be arrested."

An aide to defeated presidential candidate Mehdi Karroubi said the protests would continue as planned, while Iran's state broadcaster said a group of moderate clerics had called off the rally.

"The demonstration plan has not been cancelled and accordingly it must be held this afternoon," Reuters reported the aide as saying.

The BBC reported Mir Hossein Mousavi's wife, Zahra Rahnavard, wrote on her Facebook page that the rally would go ahead, while an announcement reportedly made on the Web site of Mousavi's Kalameh newspaper said he would make an "important" statement to the Iranian people.

Deputy national police commander Ahmadreza Radan said Iranian police will deal firmly with any illegal gatherings.

"I should emphasize that all protests held in the past week were illegal and beginning today any gathering critical of the election would be illegal," Reuters reported Radan as saying. "And police will deal with it (the protests) firmly and with determination."

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Iran's Interior Ministry reiterated the warning to Mousavi on Saturday, saying he would "be held responsible for the consequences of any illegal gatherings." The ministry also accused the 67-year-old former prime minister of supporting protests that "have lead to the disruption of security and public order," State Security Council secretary, Abbas Mohtaj, said in a statement on the ministry's Web site.

The warnings place Mousavi at a pivotal moment. He can 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.

There also are questions about Mousavi's ability to control his own followers, many who are waiting for a clear response to Khamenei's edict on Friday before Saturday's planned rally.

Meanwhile, Iran's Guardian Council was meeting Saturday to allow the three defeated presidential election candidates to voice their complaints, an Iranian news agency said.

The Fars news agency reported Mohsen Rezaie was present, but Mousavi and Karoubi had not yet joined the session.

The council, an unelected body of 12 clerics and Islamic law experts close to Khamenei, 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 is not clear, however, if they have initiated any investigations.

Hundreds of thousands of Mousavi supporters have flooded Tehran streets during several massive marches earlier this week that recall the scale of protests during the 1979 Islamic Revolution.

In a first sign of possible resistance to Khamenei's orders came shortly after nightfall in Tehran 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.

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. Some could be prepared to take their protests to the limit, but many others have no interest in an all-out mutiny against the country's Islamic system.

Khamenei was blunt Friday about what a wider fight would bring — warning those who "want to ignore the law or break the law" will face the consequences.

Police clashed with protesters in running battles around Tehran immediately after the election and the basij militia had a reported role in attacks at the university. Gunfire from a basij compound in Tehran also left at least seven people dead Monday.

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.

A spokesman for Mousavi said Friday the opposition leader was not under arrest but was 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.

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.

British Prime Minister Gordon Brown and other European Union leaders expressed dismay over the threat of a crackdown.

Both houses of the U.S. Congress approved a resolution condemning "the ongoing violence" by the Iranian government and its suppression of the Internet and cell phones.

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."

The crowds in Tehran 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 Tehran is frequently down.

The Associated Press contributed to this report.