In the Iranian capital, Tehran, witnesses say hundreds to perhaps thousands of people have been taking to the streets over the past few days to vent their frustration at the slow pace of political reform. Demonstrators have clashed with police and pro-government militants in violent confrontations that filled the streets in and around Tehran University in some of the biggest protests in the Iranian capital in years.

Initially, these protests erupted over student anger that universities would be privatized but have expanded to include a range of political demands, with some people shouting "death to Khamenei", a reference to the country's supreme ruler. The protests have continued despite stern warnings of a government crackdown against anyone who it accuses of being used by outsiders to press for political change.

Amin Sabooni is executive editor of Tehran's English language Iran Daily.

"There is a lot of frustration among our young people when it comes to the progress and the delivery of the reform process which is being blocked at several turns," said Amin Sabooni.

Despite confrontations - sometimes violent - with pro-government vigilantes, Reuters Tehran correspondent Paul Hughes says the authorities have so far allowed the demonstrations to continue.

"There hasn't been any brutal clampdown on them," he said. "The police have acted relatively well. They haven't beaten up protesters, in fact they've managed to keep some hard-line vigilantes who often do attack students and peaceful protesters away from protesters to a large degree."

These have been some of the biggest protests in Iran since November when thousands of students ignored government warnings and took to the streets of Tehran to demonstrate against the death sentence for a scholar charged with apostasy.

"People just seem to have come together to vent their anger and frustration at the generally slow pace of reform here, lack of democracy, lack of freedom of expression, poor justice system, just wide ranging demands hitting out at all kinds of political figures," said Paul Hughes. "There's a great deal of pent up frustration here. And even though the numbers of the people on the street are small, there's a large silent majority who share a lot of the same opinions. "

But how long Iranian authorities will allow the protests to go on is the question. Friday, former President Hashemi Rafsanjani charged the demonstrators were being stirred up by the United States and he urged them not to be misled by what he called U.S. conspiracies. A U.S. official denies any involvement in these protests but just last Sunday, Secretary of State Colin Powell went on Fox News and urged the Iranian people to continue pressing for pro-democratic change.

"I hope that if we keep making the case to the Iranian people that we are not your enemy, that there is a better life awaiting you if you abandon terrorism, abandon weapons of mass destruction development and put pressure on your political leaders and your religious leaders to allow more innovation within Iranian society within the Iranian economy, to start changing the policies of the past, I hope the political and religious leaders will begin to respond to this kind of pressure," said Colin Powell.

That is a view shared by Reza Pahlavi, whose late father was toppled in the 1979 Islamic Revolution.

"It's a rapidly growing and unstoppable passion," he said. "I think what we need to understand is that the Iranian people, particularly the young people today, want to end isolation, they want to join the world, they want to enjoy the freedom and the responsibilities of democracy and as such this is a movement that will not stop until we achieve that goal."

But four years ago, security forces did stop it. They were called out to put down what were some of the largest pro-reform demonstrations since the Islamic Revolution. And late Friday night, gunfire was heard in some parts of Tehran with residents quoted as saying pro-government vigilantes and riot police were out on the streets manning checkpoints, some said to be pulling people from vehicles in a strong show of force.