Some of the 31 people arrested were members of Parliament who remained there as independents, the Anatolia News Agency reported. Others were mayors.
Officials said the raids were aimed at the Kurdistan Workers Party, which is considered a terrorist group. Arrests were made in 11 towns.
The raids were organized by the chief state prosecutor in Diyarbakir, a majority Kurdish town, the agency said.
Prime Minister Recep Tayyip Erdogan had been attempting to reach out to Kurds in an effort to bring them more fully into the political system before the DTP was outlawed. He described that as an effort to undercut the PKK.
Diyarbakir Mayor Osman Baydemir suggested Thursday's raids made Kurdish reconciliation even less likely, The New York Times reported.
"If the process of elimination continues in this fashion, we say very clearly that there would not be a single person left to reach out to," he said in a statement on television.