An Iranian protester flashes the peace, or victory, sign during an anti-government protest last week. (Associated Press)

The son of the deposed shah of Iran urged nations worldwide on Thursday to withdraw their ambassadors from Tehran to protest against a relentless government crackdown on opposition demonstrators that resulted in at least eight deaths this week alone.

Reza Pahlavi, who has lived in exile since his father was toppled in the 1979 Islamic revolution, also appealed in a letter to UN Secretary-General Ban Ki-Moon for an investigation into human rights violations during the unrest.

The confrontation between Iran's clerical rulers and their opponents has returned to the streets in recent weeks, after a harsh crackdown immediately following the hotly disputed June election had all but put an end to demonstrations. Despite a continuing tough response from security forces, the opposition movement has regained some momentum.

In demonstrations Sunday, at least eight people were killed in clashes between security forces and opposition protesters on Ashoura, a sacred day for Shiite Muslims. It was the worst bloodshed since the height of the unrest in the summer.

That was followed by two days of pro-government protests Wednesday and Thursday in which crowds chanted calls for the execution of the opposition leaders. A group also posted an online threat that suicide squads were ready to assassinate those leaders if the judiciary did not punish them within a week.

Some government supporters at the two days of rallies wore white funeral shrouds to symbolize a willingness to die in defence of Iran's clerical rulers. Several hundred turned out for Thursday's demonstration in southern Tehran outside the offices of Supreme Leader Ayatollah Ali Khamenei, state radio reported.

The same day, police fired tear gas at opposition supporters trying to gather in two locations in central Tehran, said an opposition website called The Green Road. Police detained many of them, it said.

The information could not be independently confirmed because of restrictions barring journalists from reporting on opposition activity in the streets.

In an interview with The Associated Press from an undisclosed European location, Pahlavi equated the climate of the unrest in his homeland with the "revolutionary atmosphere" that preceded the fall of his father from the Peacock Throne 30 years ago, when the monarchy was replaced by an Islamic republic.

The difference, he said, is that this time the people know what they want — a secular democracy.

In the letter to Ban, Pahlavi urged the UN chief to press Iran to release those arrested and act to "halt the intolerable and increasingly dangerous march of events."

Pahlavi said that recalling ambassadors would be a "minimal but clear indication" by UN member states of their support for the rights of Iranian citizens and objections to violations of these rights by Iranian authorities.

Hundreds of protestors arrested

Iranian officials said more than 500 protesters have been arrested since Sunday's clashes and the number could be even higher. Many suspected by the government of abandoning their faith will likely be tried for apostasy — a crime punishable by death under Iranian law — as well as attempts to topple the government.

Iran has already sentenced five defendants to death in a continuing mass trial of more than 100 opposition activists and figures. More than 80 were sentenced to prison from six months to 15 years.

The police posted on their website about 100 pictures of opposition protesters involved in Sunday's demonstrations, asking the public to help identify and report them on suspicion of "damaging public property and insulting sanctities."

State prosecutor Gholam Hossein Mohseni Ejehei said the opposition leaders could be accused of supporting people who defy God by protesting against the government on Sunday. He said the leaders may face charges of "supporting apostates," or those who go against God. His comments were published in the state-owned Iran newspaper.