Kurds are calling for more political and cultural rights

Tuncer Bakirhan, the chairman of Dehap, and Ahmet Turan Demir of the smaller Free Society Party were detained on Monday morning and Sunday night respectively for questioning.

Haluk Levent, a rock singer who performed at the festival, has also been taken into custody.

Fifteen people are currently under investigation for attending the festival in the city of Gelsenkirchen, which was arranged by Kurds living in Germany.

Ankara believes that Kadek, the successor to the militant Kurdistan Workers' Party (PKK), is the organising force behind the event.

The moves by the Turkish authorities come weeks after a decision by Kadek to end a four-year ceasefire declared when PKK leader Abdullah Ocalan was arrested.

We believe this is a political lynching move Hayri Ates Free Society deputy chairman

The group accused Turkey of failing to grant Kurds greater political and cultural rights.

More than 30,000 people were killed over a 15-year period as the PKK fought for autonomy in the overwhelmingly Kurdish south-east.

No formal charges have been brought against the 15, but they face up to seven years in jail if found to have been "aiding an illegal organisation".

TV footage shown in Turkey last week showed Mr Levent performing at the festival to an audience, many of whom were carrying flags with pictures of Mr Ocalan.

Mr Bakirhan and Mr Demir both made speeches at the event.

Free Society deputy chairman Hayri Ates told AFP news agency that Mr Demir was due to testify before a state prosecutor on Monday after being taken from his home the night before.

"We believe this is a political lynching move," he said. "We are concerned that he was taken away from his home at night when the prosecutor could have just called him in for questioning during the day."