Iraq's Foreign Ministry summoned the Turkish ambassador on Saturday to demand that Turkey immediately withdraw hundreds of troops deployed in recent days to northern Iraq, near the Islamic State-controlled city of Mosul.
The ministry said in a statement the Turkish forces had entered Iraqi territory without the knowledge of the central government in Baghdad, and that Iraq considered such presence "a hostile act".
But Turkish Prime Minister Ahmet Davutoglu said the troop rotation was routine and that Turkish forces had set up a camp near Mosul almost a year ago in coordination with Iraqi authorities.
"This camp was established as a training camp for a force of local volunteers fighting terrorism," he said in a speech to a labour union that was broadcast live by NTV news channel.
ISIS overran Mosul in June 2014. A much anticipated counter-offensive by Iraqi forces has been repeatedly postponed because they are tied down in fighting elsewhere.
Iraq has urged the international community to provide more weapons and training in its battle against Islamic State, but rejects most forms of direct intervention, mistrusting the intentions of foreign powers.
Davutoglu said the camp, located some 30 km (19 miles) northeast of Mosul, was set up at the Mosul governor's request and in coordination with the Iraqi Defence Ministry.
"It has trained more than 2,000 of our Mosul brothers, contributing to the freeing of Mosul from the Islamic State terrorist organisation," he said.
Iraqi President Fouad Massoum earlier described the deployment as "a violation of international norms and law" and called on Turkey to withdraw, echoing a statement from Prime Minister Haider al-Abadi's media office a day earlier.
A senior Kurdish military officer based north of Mosul told Reuters that additional Turkish trainers had arrived at a camp in the area overnight on Thursday escorted by a Turkish protection force.
A small number of Turkish trainers was already at the camp to train the Hashid Watani (national mobilisation), a force made up of mainly Sunni Arab former Iraqi police and volunteers from Mosul.
The United States was aware of Turkey's deployment of Turkish soldiers to northern Iraq but the move is not part of the U.S.-led coalition's activities, according to defence officials in Washington.
U.S. officials made several statements last week on plans to send more U.S. troops to Iraq, prompting powerful Iraqi politicians and militias to protest against the presence of any foreign troops in Iraq without explicit permission from parliament.
Powerful Iraqi Shia Muslim armed groups have pledged to fight a planned deployment of U.S. forces to the country. Turkey has in recent months been bombing Kurdish militant positions in northern Iraq.