Iranian opposition leader Mir Hossein Mousavi made his first public appearance in a week Monday, vowing to continue his campaign against a government that he said lacks legitimacy. But his comments suggested he is abandoning massive street protests after they were quashed by a tough crackdown.

Mousavi's statements, reported on an pro-opposition news Web site, reflect his movement's struggles to survive after a wave of arrests that netted protesters, top pro-reform politicians and journalists. Hard-liners have called for Mousavi himself to be jailed. Since the crackdown, the dramatic marches that filled main streets after the disputed June 12 presidential elections have vanished.

Meanwhile, the Islamic clerical leadership is showing its determination to keep control. Supreme leader Ayatollah Ali Khamenei on Monday issued a sharp warning to Western nations not to criticize Iran over its crackdown, saying relations will suffer if they are seen as "meddling." Iranians, he said, would "unite against their enemies into one fist."

His warning appeared to be directed at world powers gathering at the G8 summit in Rome this week, who are to consider a coordinated response to Iran's turmoil.

In another sign of the regime's new toughness, the head of Iran's Revolutionary Guard acknowledged for the first time that the elite force — controlled by Khamenei — played the key role in putting an end to street protests.

Gen. Mohammad Ali Jafari vowed to continue to defend the regime. The force's intervention gave "new life" to the 1979 Islamic Revolution and "strengthened the pillars of the Islamic Republic of Iran," he said in comments carried on the state news agency IRNA late Sunday.

"We believe that the Guards, in line with the mission to defend the revolution, must play a determining role in preserving and continuing the revolution (by saying revolution, he means ruling system)," he said.

Jafari's comments suggested that the force, which usually works behind the scenes, could take a more overt hand in Iran's politics after the biggest challenge to Iran's system of Islamic clerical rule in decades. The protests erupted after Mousavi declared fraud in official results that showed a landslide victory by incumbent Mahmoud Ahmadinejad. Khamenei declared the results valid, but the protesters continued even after he said demonstrations would not be tolerated, a rare defiance of the man who holds ultimate political, religious and military power in the country.

The crackdown unleashed by the Guards, police and pro-government Basij militia killed 20 protesters and injured hundreds more. Since then, there have been no major street protests for more than a week, and Mousavi has stayed out of the public eye.

On Monday, however, he greeted well-wishers at his Tehran home for a holiday commemorating Shiism's greatest saint, Imam Ali, according to the Web site Parsine, which posted photos of him sitting in a salon with men and women in chadors.

Mousavi said the election had revealed the "flaws in the system" and that the government had been undermined despite its show of force.

"When a government doesn't take shape within the framework of the law, it has no legitimacy in the eyes of the people. This weakens the government and encourages the government to resort to violence against the people," Mousavi said, according to Parsine.

"The legitimacy of this government is in question because of people's lack of trust. This weakens the government from within even if it preserves it in appearance," he said.

But even while vowing to push ahead, he seemed to suggest his campaign was moving into a new phase, away from protests and into political action.

"That protests subsided or were silenced doesn't remove the basis of the matter. I think this opposition movement will continue," he said. "We need to make efforts to show our protest ... within the framework of the law."

Mousavi said he intends to "work with a group in an organized way," suggesting that he may set up a political party.

But his political options could be limited. Many prominent figures from pro-reform parties have been arrested and could face charges of instigating unrest, making it unclear how much authorities will tolerate opposition political activities that were long allowed. An attempt at mainstream politics could also disillusion young activists who joined protests hoping for dramatic change.

Police say more than 1,000 people were detained in the protests, though they insist most have been released. The pro-reform Web site Norooznews said late Sunday that Hamid Maddah Shourcheh, a member of Mousavi's campaign office in the northeastern Iranian city of Mashhad, died of torture during detention.

Along with the other arrests, Iranian authorities are also still holding a local employee from the British Embassy, Hossein Rassam. His lawyer said Saturday that Rassam has been charged with "acting against national security."

The detention has brought vocal protests from Britain and the European Union ahead of the G8 summit in Rome. The summit includes Russia, which has close ties with Tehran, and Germany, which has substantial economic connections to Iran. Also attending the summit is President Barack Obama, who has sought to open a dialogue with Iran and who says the option of diplomacy is still open even after the election turmoil.

Khamenei's warning on Monday appeared aimed at signaling that any of those policies could be at risk if the West takes a harsh stance on Tehran.

"Some leaders of Western countries at the level of president, prime minister and foreign minister openly intervened in Iran's internal affairs that had nothing to do with them," he said in a speech to thousands of Iranians during ceremonies for Monday's holiday.

Khamenei said Iran will pay attention to the remarks and behaviors of Western governments.

"Be careful. The Iranian nation will show reaction. We will calculate these hostile remarks, these hostile behaviors," he said. "They should know this. This behavior will undoubtedly have negative impact on future relations and interactions between the Islamic Republic and the interventionists."