Diyarbakır Mayor Adnan Selçuk Mızraklı, Mardin Mayor Ahmet Türk and Van Mayor Bedia Özgökçe Ertan -- all of whom were elected in March for the pro-Kurdish People's Democratic Party (HDP) -- were relieved of their duties, with state-appointed governors temporarily taking over their posts, according to the Interior Ministry statement.
Turkish President Recep Tayyip Erdoğan warned ahead of the March 31 municipal elections that any candidate affiliated with PKK would be replaced by Ankara.
Erdoğan's government had already removed from office more than 90 of the 103 HDP mayors, including Türk, and replaced them with government-appointed officials after the July 2016 coup attempt.
In addition, Turkey's election council decided soon after the March vote that at least four HDP district mayors would be barred from office, awarding their posts to second place finishers from the ruling party.
The statement said that the PKK, the United States, and the European Union, had been using these municipalities and their mayors for "illegal goals".
Authorities also said nine investigations were focused on Mizrakli, six investigations on Türk and seven on Ertan. Shortly before the dismissals were announced, authorities in Diyarbakir, Mardin and Van cordoned off the municipal buildings and began searching the premises, according to the BBC.
Mızraklı won 63 percent of the March vote, Türk 56 percent and Ertan 54 percent, running along with their HDP co-mayors. Mızraklı told the BBC that the will of the voters should come before all other concerns, comparing the dismissals to a coup and saying it would undermine confidence in Turkey's democracy.
"These are three major provinces," he said. "The situation will have strong repercussions for elected officials at the parliamentary level...democracy has fallen further down."