Iran's opposition still unbowed, using 'Neda' balloons as icon of protests

The unrest has exposed unprecedented rifts within Iran's clerical establishment, with Supreme Leader Ayatollah Ali Khamenei, who normally stays above the political fray, siding strongly with anti-Western President Mahmoud Ahmadinejad.

The turmoil in Iran has also put back prospects for U.S. President Barack Obama's hoped for engagement with Tehran over its nuclear programme, with Ahmadinejad's government blaming Britain and the United States for fomenting violence.

Iran's tough security crackdown has also led Obama to ramp up his previously muted criticism of Iran, with the president saying he was "appalled and outraged" by the violence.

Khamenei has declared the result of the June 12 presidential election that returned Ahmadinejad would stand and said opposition leaders would be held responsible for any bloodshed.

Some 20 protesters have been killed in the demonstrations, but police and militia have largely succeeded in taking back control of the streets this week after the most widespread anti-government protests since the 1979 Islamic revolution.