Ruled for nearly half a millennium by the Ottoman Empire, Mosul is considered by mainly Sunni Muslim Turkey to be part of its natural sphere of influence in the Middle East.
Ankara is watching uneasily the potential involvement of Shiite and Kurdish militia in the offensive, insisting thatMosul must keep its Sunni Arab Muslim majority as before IS took over the city from woefully unprepared Iraqi troops in 2014.
Iraq's Shiite-dominated government has in turn reacted angrily to the presence of hundreds of Turkish troops on its territory, ostensibly with the aim of training Iraqi troops to retake the city.
The tensions prompted President Recep Tayyip Erdogan to launch an attack on Iraqi Premier Haider al-Abadi that was venomous even by his sharp standards, telling the Iraqi leader to "know your place" and even saying "you are not at my level".
Not to be outdone, Abadi hit back by mocking Erdogan's appearance on FaceTime to rouse supporters on the night of the failed July 15 coup.
'Say in the future'
Erdogan "is concerned about the future ethnic and sectarian composition of Mosul and its environs, and wants to make sure Kurds and Shiites don't get an upper hand," said Aykan Erdemir of the Washington-based Foundation for Defense of Democracies.
Turkey has appeared hugely sensitive to any notion it has been left out of the decision-making process ahead of what is likely to be the biggest battle yet in the fight against IS.
According to the United Nations, the city still has a population of one million. Aid groups have warned hundreds of thousands could flee at the start of the operation.
Erdogan said on Friday that Turkey wanted to take part in the operation but would engage a "plan B or plan C" if it was turned down. He did not expand on the nature of the plans.
"Ankara does not want to be left out of the equation in Iraq. Erdogan is trying to make sure that he has a say in the future of the affairs in Mosul as well as Iraq," said Erdemir.
Erdemir said that after training Sunni militia to prepare for the liberation of Mosul, Ankara feared Baghdad would back Shiite militia as a key element in the planned offensive.
'Day after Mosul'
Turkey is wary of seeing a similar picture emerging as in Syria, where the United States chose a Kurdish militia detested by Ankara as its prime ally on the ground in the fight against IS.
Ankara sees the Syrian People's Protection Units (YPG) as the Syrian branch of the outlawed Kurdistan Workers Party (PKK) which has fought the Turkish state for decades and has its rear bases in northern Iraq.
"Erdogan is preparing for the day after Mosul," said Soner Cagaptay, director of the Turkish Research Programme at The Washington Institute.
"Ankara realises that Iraq will be a weak state and they want a zone of influence in northern Iraq to protect Turkey from instability coming from Iraq."
"Ankara wants to prevent the PKK from taking territory, taking advantage of a vacuum after ISIS," he added.
'Same mistakes'
Before the emergence of IS in Iraq, Turkey had major ambitions for Mosul, opening a vast consulate but then finding its entire 49 strong staff was taken hostage by the jihadists in June 2014.
The hostages were later freed in September 2015 amid murky circumstances and, symbolically, the consulate building was destroyed in a US-led coalition air strike in April 2016.
But Burhanettin Duran of the Foundation for Political Economic and Social Research (SETA) said that the United States risked making the same mistakes of poor post-conflict planning that marked its occupation of Iraq.
"The US is on the brink of a new mistake," he said, saying that by siding with the Iraqi government the United States was effectively backing Baghdad's Shiite Iranian allies.
"Omitting Turkey from the Iraqi agenda or placing the country into a secondary position due to the pressure from Iran will not create a new and peaceful Iraq."
