IRAN’S reformist opposition leader declared yesterday he was “ready for martyrdom” as his supporters fought bloody battles with police on the streets of the capital, Tehran.

Thousands confronted riot police and militiamen who fired live bullets, tear gas and water cannon in a vain attempt to quell the most serious challenge to the regime since the 1979 Islamic revolution.

Twenty-four hours after Ayatollah Ali Khamenei, the supreme leader, warned that further protests could lead to bloodshed, at least three demonstrators died and scores were beaten and injured.

The protesters were strengthened in their resolve when Mir Hossein Mousavi, the defeated candidate in the country’s presidential election, issued his most forthright challenge so far to the outcome.

In a letter to Khamenei, he claimed that the voting had been rigged months ago. Last night he warned that he could face detention and urged his followers to stage a national strike if he is arrested.

Chanting “death to dictatorship”, large crowds gathered in a boulevard linking Tehran’s Freedom Square and Revolution Square. They threw stones, knocked members of the Basiji militia off their motorcycles and set the machines on fire.

One witness described police on motorbikes beating protesters with truncheons. Helicopters hovered over the city centre, ambulances raced through the streets and black smoke rose into the sky from fires lit in metal dustbins.

Just outside Tehran, two people were killed and eight injured when a suicide bomber attacked the mausoleum of Ayatollah Khomeini, the leader of the Islamic revolution.

Regime officials blamed their opponents for the attack. Opposition sources said they believed that it could have been staged by the regime to stir up anger against them.

The demonstrators were trying to force a new election after an overwhelming victory was declared last weekend for Mahmoud Ahmadinejad, a hardline protégé of Khamenei.

Khamenei had laid his authority on the line on Friday by publicly backing Ahmadinejad and endorsing the result. Yesterday Mousavi and two other defeated candidates were invited to an emergency meeting of Iran’s Guardian Council, the body that oversaw the election, to discuss allegations of voting fraud.

The council offered to recount 10% of the votes at random but Mousavi, who refused to attend the meeting, held out for fresh elections.

As the minutes ticked down to the scheduled start time of an opposition rally at 4pm, no one was sure what would happen. On Twitter, the networking site most frequently used by protesters after the regime blocked mobile phones and texting, suspicions ran high that agents of the state were posting false messages to deter demonstrators from attending.

Riot police flooded key areas. The city appeared calm. Then a message appeared on the Facebook site of Zahra Rahnavard, Mousavi’s wife, stating simply: “Demonstration on Saturday at 16.00 in Tehran and all around the world please.”

Crowds headed towards the university, Revolution Square and Freedom Square in the centre of the city. As in the 1979 uprising against the shah, many were from the educated middle class.

Soon an Iranian journalist, writing on Twitter in broken English, was reporting “Streets full of population”.

Later he tweeted that the militia had attacked the protesters with batons. Then: “Hard conflict between the people and the special guard.”

Videos made by people on the streets were said to have recorded protesters chanting, “Death to Khamenei”. Never before had the supreme leader faced such open hostility from his compatriots.

Soon afterwards a Twitter source said “the street is full of rocks and fire” and police or Basiji were “shooting directly to the people in Azadi St”.

Eyewitnesses described fierce clashes, telling of incidents where 50 or 60 protesters were seriously beaten by police and taken to hospital in Tehran. People could be seen dragging away bloodied comrades.

By late afternoon one eyewitness told The Sunday Times that at least 20 shots had been fired and many protesters had been beaten. Others claimed more drastic action.

The regime had already arrested 2,000 members of the opposition by Thursday, including 100 senior figures, and by last night the figure had risen sharply.

If the clashes continue, Khamenei may call on the Islamic Revolutionary Guard to quell dissent. But whether they will fight civilians is open to question. They are charged with protecting the revolution, not the supreme leader. Some are loyal to Hashemi Rafsanjani, the powerful former president who is backing Mousavi.

Last week one young member of the Revolutionary Guard said as he watched the demonstrators: “I will not be able to fire on these people. Maybe some of us will, but I won’t.”

Although details of casualties were hard to obtain because of the restrictions on the media, disturbing video film apparently taken from the riots appeared late yesterday. One clip showed a young women lying in the road attended by passers-by. She had been wounded in the leg and blood was pouring from her mouth. She appeared to be dying.

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