The Iranian government gave civil servants a day off to attend the rallies. Here, a woman holds a poster of Ayatollah Ali Khamenei in Revolution Square in Tehran on Wednesday. (Vahid Salemi/Associated Press)

Tens of thousands of protesters rallied in the streets of Tehran Wednesday in support of the Iranian government and Ayatollah Ali Khamenei, the country's supreme leader.

State-sponsored rallies were being held across Iran as a show of strength following days of opposition demonstrations.

Sunday's clashes between protesters and riot police were the most violent since the aftermath of June's disputed presidential election. Eight people were killed and 500 arrested in anti-government protests, held during the observance of Ashura, a solemn Shia festival, the government said.

Of those detained, 300 remained in custody, the official IRNA news agency said.

Those attending counter-demonstrations in the Iranian capital chanted "Death to Mousavi," a reference to opposition leader Mir Hossein Mousavi. Some shouted "Rioter hypocrites must be executed" and held up a banner that read: "We sacrifice our blood for supreme leader."

Several of the demonstrators who gathered in Enqelab (Revolution) Square signed a scroll to deliver to the judiciary chief, condemning the opposition leaders.

Iran's police chief, Gen. Ismail Ahmadi Moghaddam, has vowed to crack down on any further opposition rallies, while the Speaker of the country’s parliament, Ali Larijani, urged justice officials to "mete out the harshest punishments to anti-revolutionary figures with no mercy."

The government is blaming foreign influences for the recent unrest. President Mahmoud Ahmadinejad, quoted by IRNA, called the anti-government protests "a theatre play by the Zionists and the Americans."

With files from The Associated Press