Around 200 people, including HDP lawmakers, gathered near Diyarbakir town hall late Tuesday to protest the arrests
The two co-mayors of Diyarbakir, the biggest Kurdish-majority city in southeast Turkey, have been arrested as part of a "terrorism" enquiry, security officials said.
There was a heavy police presence around the town hall following the arrests of Gultan Kisanak and Firat Anli, who together lead a city that has been rocked by clashes between security forces and members of the outlawed Kurdistan Workers' Party (PKK).
Dozens of police were surrounding the town hall with light armoured vehicles and trucks loaded with water cannon as officers searched the building, an AFP correspondent said.
Kisanak was held at the local airport and Anli at his home, officials told AFP.
Turkish President Recep Tayyip Erdogan has repeatedly warned that local officials accused of offering logistical help to the PKK -- which Ankara considers a terrorist organisation -- would be prosecuted.
The pro-Kurdish Peoples' Democratic Party (HDP) condemned the arrests and called for supporters to join a protest at 0800 GMT Wednesday.
"We condemn the arrests of Gultan Kisanak and Firat Anli. We demand their immediate release," the party said on its Twitter feed.
Around 200 people, including HDP lawmakers, gathered near Diyarbakir town hall late Tuesday to protest the arrests.
Last month, 24 mayors suspected of links to the PKK were suspended and replaced with officials close to Erdogan's ruling Justice and Development Party (AKP).
The controversial move sparked fresh clashes, with one of the new administrators shot dead in Van, eastern Turkey, on October 16.
More than 40,000 people have been killed since the PKK first took up arms in 1984 demanding an independent state for Kurds.
Since then the group has narrowed its demands to greater autonomy and cultural rights.
Violence flared again between Kurdish rebels and government forces last year, shattering a 2013 ceasefire reached after secret talks between PKK leader Abdullah Ocalan and the Turkish state.