Iran's opposition has called for fresh street protests tomorrow to commemorate the death of two pro-democracy youths killed during anti-government rallies held last week.

The move came after the Iranian regime launched a new campaign to silence the leaders of the Green Movement in what was seen as the most rigorous crackdown on the opposition since the post-election unrest in 2009.

Opposition websites reported that the rallies are aimed at fighting religious dictatorship and voicing support for former presidential candidates Mir Hossein Mousavi and Mehdi Karroubi.

"In response to the brutal suppression and killing of the supporters of the Green Movement, we will go out in streets in major squares [of Tehran and other big cities] on Sunday which will mark the seventh day after the death of our martyrs," the official website of Mousavi, Kaleme.org, said.

Mousavi and Karroubi came under fire after they issued a call for renewed street protests in solidarity with demonstrators in Egypt and Tunisia. The Iranian regime has been criticised by the opposition for hailing the Arab revolts abroad, while refusing to give permission for a peaceful demonstration at home.

In response to the request, thousands of protesters, inspired by the uprisings in Egypt and Tunisia, marched in Iran's capital and other big cities last Monday in defiance of warnings by the regime and a heavy security presence in what was seen as the Iranian opposition's first attempt in more than a year to hold anti-government protest.

Two demonstrators, Saane Zhaleh, 26 and Mohammad Mokhtari, 22 were killed in Tehran during clashes between the protesters and security officials who fired teargas, wielded batons and opened fire to disperse the crowd. Dozens were injured and at least 250 were arrested.

After Monday's protest, an overwhelming majority of the Iranian parliament called for Mousavi and Karroubi to be executed and put on trial. "If you have the courage, put me on trial, but on a public trial and let the media report what I say in that trial," Karroubi said in response, according to his official website, Sahamnews.org.

Opposition websites also reported that both opposition leaders were completely cut off from outside world.

Speaking to the Observer, Ardeshir Amir-Arjomand, a spokesman for Mousavi and Karroubi, said: "They are both placed under house arrest and there's no information on their situation and health. The road to Mousavi's house is blocked by security forces who have not given permission to anybody to visit him for the past whole week, including his daughters. They are both denied access to the outside world."

He added: "We are very worried for Mousavi's health because he is given food by the security officials and we don't have any knowledge of what they are providing him with."

In reaction to Monday's protest, authorities in Iran hijacked the funeral of Zhaleh – a theatre student who had been attending Tehran University of Arts – bussing in hundreds of pro-government supporters and banning his own family from attending.

On Friday, hardline cleric Ahmad Janati, called in a sermon for Mousavi and Karroubi to be completely isolated.

"The doors of their houses should be shut and their telephone lines and internet be cut so that they can no longer have any contacts and give any messages," he said. "Those who say the seditionists [Mousavi and Karroubi] should be executed should bear in mind that the [reformist leaders] are already executed," he added.