Assassinations, attempted murders and abductions have targeted more than 70 activists since a pro-democracy protest movement erupted against government corruption and incompetence in 2019.

"We're here to say that we want to end impunity in Iraq," Hussein Al-Faili, an 18-year old student, told AFP from Firdous Square, a key protest site.

"We want freedom! This revolution started because of this and we won't stop until we win."

Dozens also turned out in Nasiriyah, a rebellious Shi'a city in southern Iraq where tensions have been running high following a hospital fire that killed at least 60 people on Monday.

Prime Minister Mustafa Kadhemi on Friday announced the arrest of four suspects in the point-blank shooting of prominent academic and government adviser Hisham al-Hashemi a year ago.

Iraqi state television broadcast brief clips late Friday of the alleged confession of Ahmed al-Kenani, a 36-year-old police lieutenant, who said he had used a pistol to murder Hashemi.

A security source told AFP Kenani was affiliated with Kataeb Hezbollah, a hardline pro-Iran armed faction.

But Faili said the arrests were not enough.

"We want the big man who ordered the murder," Faili said.

The boisterous crowd at Firdous Square listened to a young man sing a melancholic medley.

That was followed by a recording of a poem by iconic young activist Safaa Saray, who died in 2019 after being struck with a tear gas canister to his head during a demonstration.

The mostly young protestors on Sunday chanted against "political parties, traitors and militias" as others tearfully remembered their assassinated comrades.

Another young woman, also a student, lambasted the presence of "militias and Iranian intrusion in Iraq".

Iraq, still battered and impoverished after the 2003 US-led invasion and the turmoil that followed, has been a battleground for influence between arch-foes Washington and Tehran, which has backed paramilitaries and politicians.

Activist Shatha Al-Qaisi said "this campaign... seeks to gain support from all over the world to stop the bloodshed. It's not a politicised movement".