President Recep Tayyip Erdogan on Friday ruled out introducing any federal system in Turkey, after an angry backlash to comments by an adviser from nationalists key to his success in this weekend's referendum.
Turks will decide on Sunday whether to approve boosting Erdogan's powers under an executive presidency, which would also see the role of prime minister axed.
Erdogan's advisor Sukru Karatepe was accused this week of suggesting in an Ankara publication that, if approved, the changes could lead to a federal system in the country but the government said his comments were misunderstood.
"Brothers and sisters, I always have been and will always be the biggest supporter and biggest defender of Turkey's unitary structure," Erdogan said during a 'Yes' rally in the central Turkish province of Konya.
"A federal structure, federation, this or that: none of this is on our agenda and it will not be," he added.
Erdogan was forced to reject such changes after he was slammed by far-right Nationalist Movement Party (MHP) leader Devlet Bahceli for his adviser's remarks.
A federal system is an anathema for nationalists who believe in the unbreakable unity of the Turkish state and are particularly against the creation of any Kurdish region in the southeast. 
Turkey is made up of 81 provinces, whose governors are directly appointed by Ankara.
Bahceli, who has thrown his support behind the government's proposed constitutional changes, said if it had been his advisor, he would have removed him from his position.
"If the president is not speaking out, if he acknowledges it, then what would be the decision of nationalists -- who are against a federal structure and support a unitary one -- be (in the referendum) in two days?" Bahceli told NTV broadcaster on Thursday night.
Erdogan responded by asking: "Have you heard such a thing from me? No."
Prime Minister Binali Yildirim insisted the ruling Justice and Development Party (AKP) was as dedicated to a unitary structure as the nationalists and vowed to resign if the changes led to such a system.
The government is keen to assuage fears of nationalists who are crucial for Erdogan to win the referendum, which polls and experts say is hotly contested.
Karatepe later told reporters that he would "never accept any federational or federal system in Turkey".
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