Iraq's top Shi'ite cleric Grand Ayatollah Ali al-Sistani on Friday criticized the deployment of Turkish troops and tanks to the country's north without Baghdad's approval.
Baghdad has demanded that Ankara remove the newly-deployed forces, which were sent to a base near the city of Mosul in northern Iraq, but Turkish President Recep Tayyip Erdogan said a withdrawal was "out of the question."
No country should "send its soldiers to the territory of another state under the pretext of supporting it in fighting terrorism without the conclusion of an agreement... between the governments of the two countries," Sistani said in remarks delivered by a representative at Friday weekly prayers.
Turkish Prime Minister Ahmet Davutoglu has defended the deployment as an "act of solidarity" and said: "When the threats (to the trainers) increased, we sent troops to protect the camp."
Turkey has been training forces opposed to the Islamic State (ISIS) jihadist group, which overran large areas north and west of Baghdad last year, at the base.
But it also gives Turkey a foothold in an area where a major ground operation against ISIS is eventually to take place, and where its archfoe, Turkish Kurdish rebel group the Kurdistan Workers' Party, has also sought to expand its presence.
Iraqi Prime Minister Haider al-Abadi, whose high-profile reform program has accomplished little in the way of lasting change, can ill afford another setback now, but repeated calls for a Turkish withdrawal have gone unheeded.
Earlier this week, Iraq gave Turkey 48 hours to remove the forces, but the deadline passed without Ankara doing so and Erdogan subsequently ruled it out.
"What they do in Bashiqa and at the camp is training," Erdogan told a news conference in Ankara late on Thursday, referring to the area where the base is located.
"The number of our soldiers will increase or reduce according to the number of peshmerga (Iraqi Kurdish forces) who are trained. (Their) withdrawal is out of the question," Erdogan said.
Top Iraqi officials reiterated their demand for a withdrawal during talks on Thursday with a Turkish delegation that included foreign ministry under secretary Feridun Sinirlioglu and intelligence chief Hakan Fidan, officials said.
Baghdad is also seeking United Nations condemnation of the deployment.
AFP contributed to this report.