Could a domino effect sweep more leaders from power as unrest has been spreading throughout the region ?

Long-simmering unrest over the disputed 2009 presidential election boiled over again on 14 February.

Thousands of people heeded calls by the two main opposition leaders to rally in the capital Tehran in solidarity with pro-democracy protests across the Middle East.

Security forces cracked down on the protest. Two people were killed and many more injured.

Rallies held in the days following, as well as on 20 February, were also suppressed. In further demonstrations on 1 March, the opposition claimed that 200 people were arrested.

Supporters of the government have been calling for the opposition leaders, Mehdi Karroubi and Mir Hossein Mousavi, to be executed. The pair have been placed under house arrest.

Iran's complex and unusual political system combines elements of a modern Islamic theocracy with democracy. Its President, Mahmoud Ahmadinejad, is a hardliner who has vowed to put down any protests.

Meanwhile, there has been speculation in recent months about the internal dynamics of the regime, after tensions appear to have increased between President Ahmadinejad and Supreme Leader Ayatollah Ali Khamenei.

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