within the strict boundaries of the Islamic Republic.

And for this year's parliamentary elections, which are due to be held in February, thousands of potential candidates have again been disqualified, including 90 current lawmakers.

Any candidates from groups opposed to the Islamic Republic, or who want to change the existing system altogether, are not allowed to run.

image copyright Getty Images image caption Ayatollah Khamenei sits at the top of the Islamic Republic's political structure

The Guardian Council can also bar any would-be presidential candidates, and veto any legislation passed by parliament if it is deemed to be inconsistent with Iran's constitution and Islamic law.

Ayatollah Khamenei, who is positioned at the top of Iran's political power structure, appoints half of the members of this body.

The Supreme Leader also controls the armed forcesand makes decisions on security, defence and major foreign policy issues.

So in practice, the president and the parliament in Iran - even if they support change - have limited powers.

There are also opposition movements who want greater autonomy for ethnic minorities like the Kurds, Arabs, Baluchis and Azerbaijanis.

Some of these groups - like the Democratic Party of Iranian Kurdistan - are armed and have fought for decades against the Iranian state.

Does the opposition have leaders?

There has been a movement pushing for reform in Iran for years, with Mohammad Khatami, the former president, as its figurehead.

In office from 1997 until 2005, Mr Khatami brought in limited social and economic reforms, and put out feelers to Western countries.

More extensive changes, however, were blocked by conservative interests, and Mr Khatami himself