Iraq says Turkey deployed troops and tanks to a base in the country's north last week without its permission, sparking a diplomatic uproar between Baghdad and Ankara.
Turkey insists the forces were deployed to protect trainers working with Iraqi forces at the site, but Baghdad has repeatedly demanded their withdrawal and complained to the UN Security Council.
Groups within the Hashad al-Shaabi, or Popular Mobilisation forces, which are dominated by Iran-backed Shiite militias, called for the demonstration against the Turkish military presence.
Iraqi Prime Minister Haider al-Abadi should have struck "with an iron fist at the beginning," rather than make concessions to Massud Barzani, the leader of Iraq's autonomous Kurdish region, and others, he said.
"But we are not here to doubt the ability of our commander-in-chief, and as a brigade we are ready," said Rubaie, who wore a military uniform and had a large Iraqi flag on a pole resting on his shoulder.
Not all the demonstrators were fighters, including businessman Hussein al-Samawi, who came from the city of Samawa, south of Baghdad, to take part.
"We agree with every step the prime minister is taking right now," said Samawi, who was dressed in a suit.
"We have to pursue the political track, but if it doesn't work, force will be the only option," he said.
The demonstration was mostly attended by young men in military uniforms and was well organised, with large processions converging on Tahrir Square in central Baghdad.
Iraq yesterday circulated a letter among the members of the UN Security Council to express "growing alarm" that the problem was not being resolved.
