Story highlights Supporters of Shiite cleric Muqtada al-Sadr clash with security forces in Iraq's capital

Iraqi Prime Minister Haider al-Abadi orders an investigation

(CNN) Protests by supporters of a powerful Iraqi Shiite cleric turned fatal Saturday in Baghdad.

A police officer was killed and seven others wounded during clashes between supporters of Muqtada al-Sadr and security forces, Baghdad's security operations command said Saturday.

The cleric has called for the reform of Iraq's election commission, which he has accused of corruption, and demonstrators had gathered to support him.

The rally reached the edge of the fortified Green Zone , an area housing government buildings and foreign embassies.

Video of the rally showed police firing tear gas at the protesters.

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