Iraqis have been staging weekly protests since July. The movement that stemmed from exasperation over power cuts in the searing summer heat gradually led to broader demands for political reform.
Prime Minister Haider al-Abadi, with backing from the country's most revered Shiite religious cleric, announced a reform package but change has been slow to materialise and the protests have continued.
"Baghdad will no longer be silent," chanted thousands of protesters in the capital's Tahrir (liberation in Arabic) Square.
Regular protesters -- dominated by secular groups, journalists, artists and social activists -- were joined Friday by supporters of Shiite cleric Moqtada Sadr.
"Our participation in the protests continues because the scope of Abadi's reforms is limited," said Bashir al-Saadi, a young Sadr supporter.
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He claimed the prime minister was restrained in his efforts by his own Dawa party -- of which his predecessor and rival Nuri al-Maliki is also a member -- and other parties.
Some civil society activists who have taken part in the protest movement since it began argued that the Sadrists should put their own house in order before campaigning against corruption in the state.
"They are part of the government so they should start by removing their own ministers and MPs in front of the Iraqi people," said Abu Ammar, 51.
"Right now they are protesting against themselves, it doesn't make sense," he said, surrounded by protesters waving the national flag and holding up banners demanding bread, freedom and social justice.
The demonstration, held under heavy protection from the police, army and the Sadrists' own security service, passed off without incident.
Several smaller protests were also held in other cities, including the main southern hub of Basra, the Shiite shrine city of Karbala and Nasiriyah.