Most of those detained in the latest sweep were lawyers, according to media reports.

The investigation began two years ago and hundreds of people, including elected mayors, are already standing trial on charges of ties to the Kurdistan Workers Party (PKK) guerrilla group.

In Diyarbakir, the main city in Turkey’s restive mainly Kurdish southeast, police held 30 people, including members of the pro-Kurdish Peace and Democracy Party (BDP), officials said.

The BDP formed a parliamentary block of 29 deputies in the national assembly after a parliamentary election in June.

The mass detentions could hinder efforts to forge political consensus for a new constitution that was expected to partly address the issue of Kurdish rights.

Among those detained on Tuesday was a deputy mayor of a Diyarbakir district and the BDP’s provincial leader. Police also searched BDP offices in the city and seized computers and documents, and set up checkpoints at entrances to the city.

Simultaneous raids were also conducted in the capital Ankara and the western cities of Istanbul and Bursa, they said.

Last month more than 100 people were detained in similar raids which coincided with a surge in PKK attacks on Turkish security forces. These triggered military strikes against guerrilla bases in the mountains of neighboring northern Iraq.

The investigation is focused on an organization called the Union of Kurdistan Communities (KCK), which the PKK established in 2005 with the aim of creating its own Kurdish political system, according to a 2009 indictment.

Some 150 politicians and activists are already being tried in Diyarbakir where a large courtroom has been specially built. Similar trials are being held in other cities across Turkey.

The European Union, which Turkey is aiming to join, is closely watching the cases and their human rights implications.

More than 40,000 people have been killed in the conflict between the PKK and the state since the militants launched their armed insurgency in 1984. Turkey, the United States and European Union list the PKK as a terrorist organization.