Shi'ite Muslim cleric Muqtada al-Sadr's party was the biggest winner in an Iraqi election on Monday, increasing the number of seats he holds in parliament, according to initial results, officials and a spokesperson for the Sadrist Movement.

Former prime minister Nouri al-Maliki looked set to have the next largest win among Shi'ite parties, initial results showed.

Iraq's Shi'ite groups have dominated governments and government formation since the US-led invasion of 2003 that toppled Sunni dictator Saddam Hussein and catapulted the Shi'ite majority and the Kurds to power.