The mayors of the Kurdish-majority Hakkari, Yuksekova, Ercis and Nusaybin, were held over “terrorism” links, state-run Anadolu news agency said, without elaborating.
All are members of the People’s Democratic Party (HDP). The party also confirmed their arrest.
Six other municipal officials were also arrested, Anadolu said.
Turkish President Recep Tayyip Erdogan and his government accuse the HDP of ties to the Kurdistan Workers’ Party (PKK), which has waged a decades-long armed struggle against the Turkish state for autonomy.
The HDP denies links to “terrorism” or the PKK.
While most of Turkey’s opposition parties have backed its ongoing operation, the HDP has called for it to stop, describing it as an “invasion attempt”. The HDP says the operation is an attempt by the government to drum up support amid declining public backing.
Ankara launched its offensive in Syria on Wednesday, aiming to push back “terrorist” elements from the Turkey-Syria border and establish a “safe-zone” to resettle some of the 3.6 million refugees it hosts.
The border region, east of the Euphrates River, was controlled by the Kurdish-led Syrian Democratic Forces (SDF). And Ankara considers the People’s Protection Units (YPG), which form the backbone of the SDF, as extensions of the PKK.
The PKK is designated a “terrorist” organisation by Turkey, the United States and the European Union. Nonetheless, Washington and Brussels do not consider the YPG and its political-wing – the Democratic Union Party (PYD) – as “terrorist” groups.
Since Turkey and its Syrian allies launched the assault in Syria, the HDP said 151 of its members, including district officials, had been arrested.
Last week, Turkish police also launched criminal investigations into the HDP’s cochairs over their criticism of the military operation and started investigations into more than 500 social accounts over “terrorist propaganda” criticising the offensive.
Authorities launched similar investigations after each of Turkey’s two previous cross-border operations into Syria.
More than 300 people were arrested for social media posts, criticising Turkey’s offensive into northern Syria in January 2018.