The top leaders of Iran's elite Revolutionary Guard publicly acknowledged they had taken over the nation's security during the post-election unrest and warned late Sunday, in a threat against a reformist wave led by Mir-Hossein Mousavi, that there was no middle ground in the ongoing dispute over the reelection of President Mahmoud Ahmadinejad.

Maj. Gen. Mohammad Ali Jafari, commander of the elite military branch, said the guard's takeover of the nation's security had led to "a revival of the revolution."

"These events put us in a new stage of the revolution and political struggles, and all of us must fully comprehend its dimensions," he said at a Sunday press conference, according to reports that surfaced today.

"Because the Revolutionary Guard was assigned the task of controlling the situation, [it] took the initiative to quell a spiraling unrest. This event pushed us into a new phase of the revolution and political struggles and we have to understand all its dimensions."

Meanwhile, the guard's commander in chief, Supreme Leader Ali Khamenei, warned Western leaders against exploiting the nation's political turmoil for their own ends.

"The Western governments should be careful about their hostile words and behavior because the Iranian nation will react," he told supporters on the occasion of the birthday of the Shiite saint Imam Ali. "We take into account the interfering words and behaviors of these governments and their attitudes will definitely affect the future of Islamic Republic of Iran's relations with them.'

His speech, broadcast on state television, followed Vice President Joe Biden's comments that the U.S. would not stop an Israeli attack on Iran's nuclear facilities.

"Even if the Islamic Republic leaders are at odds on certain affairs, they are united against the enemy as far as the safeguarding the country's independence is concerned," he said.

Many officials had said that the Revolutionary Guard had taken control of the nation's security in the wake of weeks of unrest that followed the June 12 vote, which opposition leaders claimed was stolen by Ahmadinejad, the incumbent.

Jafari's comments came the closest yet to publicly acknowledging what government supporters describe as a heroic intervention by the Revolutionary Guard and critics decry as a palace "coup d'etat" instigated by military elites loyal to Khamenei.

Opposition figures and protesters are preparing for massive nationwide rallies called for Thursday, the 10th anniversary of a 1999 attack by pro-government militiamen on the dormitories of Tehran University that led to weeks of political unrest.

The Basiji militia, which was formally placed under the command of the Revolutionary Guard earlier this year, is also said to be mobilizing to crack down on the demonstrators.

Over the weekend, Grand Ayatollah Assadolah Bayat Zanjani launched a broadside against the mass arrest of reformist activists and protesters.

"Every healthy mind casts doubt on the way the election was held," said the high-ranking clericin a statement distributed online. "More regrettable are post-election large-scale arrests, newspaper censorship and website filtering, and above all the martyrdom of our countrymen whom they describe as rioters."

The families of those detained spoke out harshly against the government. "My father is a defender of pure Islam," Mehdi Saharkhiz, the son of journalist Issa Saharkhiz, who remains in prison, wrote today, Father's Day in Iran, in a letter posted to various websites.

"My father has done his utmost to defend the republican nature of the regime," he wrote. "He wants to establish religious democracy, but you and your accomplices prefer your mundane interests to anything else."

The Revolutionary Guard is trying hard to stifle such criticism.

"Today, no one is impartial," Gen. Yadollah Javani said at the Sunday news conference, according to the Islamic Republic News Agency. "There are two currents -- those who defend and support the revolution and the establishment, and those who are trying to topple it."

The uniformed Revolutionary Guard leaders, joined by the turbaned cleric Ali Saedi, Khamenei's representative, said they would play a more active role in defending the Islamic Republic's core values, though they insisted this should not be interpreted as meddling in politics.

"The Revolutionary Guard is tasked with defending the revolution and it has to play a determining role in protecting and eternalizing the revolution," said Jafari, in comments posted to government websites. "Such an attitude does by no means mean interference with politics."

The guard and its allies have rarely refrained from entering daily politics. As Mousavi's supporters described plans to create a new political party Sunday, an editorial in today's editions of Sobh Sadegh, a newspaper close to the Revolutionary Guard, argues that the powerful Guardian Council should bar "liars and rabble-rousers who were running for president" from taking part in electoral politics.

But Khamenei's speech contained some conciliatory gestures toward Mousavi supporters, who include reformist clergy and politicians. After his deputies for weeks equated peaceful demonstrators with rioters, Khamenei said it was foreigners had described Iranian people as rioters.

"Rioters were a minority who received budget allocated by some Western governments," he said.

"It is natural that some Iranians feel depressed and sad due to the failure of their preferred candidate," he said. "The Islamic regime feels compelled to deal with those who threaten people and disturb their life and serenity. But the authorities should be careful to not mistake enemy for friend and consider friends as enemies just for a single error."