TEHRAN - One of Iran's most prominent opposition leaders was placed under house arrest Thursday, with security agents posted at the entrance saying they would stay there until a possible anti-government protest has passed, the cleric's Web site reported.

"Only his wife is being allowed into the house," Sahamnews.org said. "This probably has to do with the protest scheduled for Monday, Feb. 14."

But the measure also appeared intended to prevent Mehdi Karroubi, a former head of parliament who has become highly critical of Iran's leaders, from participating in a state-backed rally Friday to celebrate the 32nd anniversary of the country's Islamic revolution.

Last year, Karroubi crashed the official celebrations, together with supporters of the grass-roots Green Movement, triggering minor skirmishes between the opposition activists and security forces.

Karroubi and Mir Hossein Mousavi, who both unsuccessfully challenged President Mahmoud Ahmadinejad in a June 2009 election, sought permission Sunday to hold a rally Monday. In a letter posted on Sahamnews on Sunday, they invited people "to express solidarity with . . . the freedom-seeking revolts of the people of Tunis and Egypt against despotic regimes." Since the unprecedented and deadly anti-government protests after the presidential election, no such permits have been given.

There have been no reports of Mousavi being placed under house arrest.

The call for a protest coincides with strong support by the Tehran government for the uprisings in Tunisia and Egypt, which it says have been influenced by Iran's 1979 Islamic revolution. The opposition, which has had no visible street presence since last year's revolution anniversary, has also embraced the cause of the Egyptian and Tunisian demonstrators but describes them as fighting "against dictatorships."

On social-networking sites and foreign-based Farsi satellite television stations, opposition supporters are saying they plan to demonstrate Monday, but crowds have failed to materialize at some scheduled protests in the past, and paramilitary forces using tear gas and batons have dispersed several large anti-government demonstrations. A Facebook page dedicated to the Monday event has more than 20,000 followers, but it is unclear how many of them are in Iran.

Although the government has not officially banned Monday's protest, there are clear signs that it will not be allowed to proceed. "The seditionists are nothing more than a corpse, and we will strongly suppress any movement or action by them," Hossein Hamedani, a senior commander of the Revolutionary Guard Corps, said Wednesday, according to the official Islamic Republic News Agency. "We will treat them as anti-revolutionaries and spies."

In a sign of a wider crackdown ahead of the rally and the protest, Sahamnews reported the arrest since Wednesday night of two Karroubi allies, Taghi Rahmani and Mostafa Mirahmadizadeh. Also Thursday, Mousavi's Web site, Kaleme.org, reported the detention of a close Mousavi ally, Mohammad Hossein Sharifzadegan.

State officials have suggested that anyone wanting to support the Egyptians and Tunisians can join the state-backed rally Friday.

"The designation of another date [for protests] shows that these gentlemen [Karroubi and Mousavi] have separated their path from the people," national prosecutor Gholam Hossein Mohseni-Ejei told the semi-official Mehr News Agency on Wednesday. "This is a political action, but the people of Iran are clever and, if necessary, will respond."

Special correspondent Kay Armin Serjoie contributed to this report.