"The ugly massacre that took place in Treimsa town, in Hama province, provokes feelings of concern and condemnation," Nuri al-Maliki said in a statement published on his official website.

"This reprehensible crime, which we condemn strongly ... should be an additional incentive for everyone to abandon the methods of violence, murder, revenge and terrorism in solving problems," Maliki said.

He said the killings should urge people to accelerate finding a peaceful solution to the 16-month-long Syrian crisis.

The killings on Thursday have sparked an international outcry, and added urgency to deadlocked Security Council negotiations on a Syria resolution.

Iraq, which has a 600-kilometre (375-mile) border with Syria, has voiced support for a peaceful solution to the Syrian crisis which initially began in February 2011.

The three-hour march, which included calls for the government to improve basic services, began at the national theatre and headed towards the party's headquarters in central Baghdad amid a heavy security presence.

The demonstrators carried the flag symbolising the 1958 revolution, pictures of Abdul Karim Qassim, the Iraqi republic's first president and banners calling for increased jobs opportunities and better services.

On July 14, 1958, Brigadier General Qassim led a coup overthrowing the monarchy that had ruled Iraq since the modern country was founded in 1921.

Unlike many Iraqi protests, which often see angry youths chanting anti-government slogs, Saturday's Communist rally began with music and traditional dances and ended with poetry praising the revolution and Qassim.

"The 14th of July revolution will be in the hearts of Iraqis even after hundreds of years and the name of the leader Abdul Karim Qassim will be held high because he was honest and sacrificed himself for Iraqis," said Jowada Abdulkadhim, a party member.