Turkey has removed three elected mayors from office and detained more than 400 people as part of a crackdown over alleged links to Kurdish militants.
The mayors, who were elected in March, are accused of spreading "terrorist propaganda" and "financing terrorism".
Ankara says they - and the many others detained - have ties to the outlawed Kurdistan Workers' Party (PKK).
There are fears that the move could escalate tensions in the mainly Kurdish south-east regions of the country.
The operation on Monday saw teams of officers conducting raids in 29 provinces across Turkey.
Those detained include the mayors of Diyarbakir, Mardin and Van provinces - all of whom secured large majorities in the March elections.
They are members of the opposition pro-Kurdish Peoples' Democratic Party (HDP), but are accused of sharing links with the PKK.
The charges reportedly include renaming local streets and parks after imprisoned PKK members and offering jobs to the relatives of militants, Turkey's interior ministry said in a statement.
"Through judicial and administrative investigations, our ministry suspended mayors who were identified and proven to be engaged and affiliated with terrorist organisations," the ministry said.
It added that the officials were "deliberately and wilfully nominated as mayoral candidates in some municipalities".
But the HDP has labelled the decision a "blatant move to hijack electoral will" and has called on all opposition parties to raise their voice in protest.
The mayor of Diyarbakir, Selcuk Mizrakli, said the move by the Turkish government "disregards the will of the people", AFP news agency reported.
The vice-president of the secular Republican People's Party (CHP), Ozgur Ozel, tweeted: "Once again the ruling AK [party] chose fascism instead of democracy."
In June, the AK party suffered defeats in Turkey's major cities, losing control of Istanbul after a re-run of the city's mayoral election in a stinging blow to Turkish President Recep Tayyip Erdogan.
The Kurdish PKK has waged an insurgency in Turkey for more than three decades, costing more than 40,000 lives.
The group is blacklisted as a terror organisation by Ankara and its Western allies, and there have been several military operations against them since 2015.