The trial coincides with cautious steps by the Turkish government to grant wider rights to its sizeable Kurdish community with the hope of ending a deadly 26-year Kurdish insurgency.

Heavy security was in place outside the courthouse in Diyarbakir, the regional capital of the mainly Kurdish southeast, for the trial which is also being followed by intellectuals and rights activists from Europe.

The 7,500-page indictment accuses the suspects of involvement in the Kurdistan Associations Union (KCK), which prosecutors describe as a terrorist group that acts as the urban extension of the armed Kurdistan Workers' Party (PKK).

It calls for jail terms ranging from five years to life in jail on various charges including "leadership and membership of a terrorist organisation", "undermining the state's unity", "spreading terrorist propaganda" and "aiding an abetting a terrorist organisation".

Among the suspects is Osman Baydemir, the popular mayor of Diyarbakir who risks up to 36 years in jail on various charges.

Eleven other regional mayors from Turkey's main Kurdish party -- the Peace and Democracy Party (BDP) -- and former lawmaker Hatip Dicle are among the defendants.

In Monday's hearing, defence lawyers demanded that they be allowed to make their arguments in Kurdish. The judges adjourned the case until the afternoon to rule on the demand.

The indictment says the KCK recruited militants for the PKK, made all major decisions shaping Kurdish political life such as the selection of candidates for municipal and parliamentary seats, syphoned off money from Kurdish-held local administrations and orchestrated violent street protests.

Turkey's main Kurdish political parties allegedly acted in line with KCK directives and the organisation was said to be influential enough to slap sanctions on those who disobeyed its decisions.

Kurdish mayors were allegedly required to donate to the KCK the two first salaries they received upon election, while municipal employees were required to donate part of their salaries every month.

The indictment said the KCK was headed by an 11-strong board led by Sabri Ok, a senior PKK militant known to be based in Europe who is being tried in absentia.

The charges were brought as part of a massive crackdown on Kurdish activists in the southeast since last year, in which a number of weapons were seized.

Defence lawyers and Kurdish activists have slammed the trial as a move to "silence Kurds".

"Our clients are being tried as unarmed members of an armed group," lawyer Meral Danis Bestas told reporters last week.

"This is a political trial aimed at silencing Kurds... This trial will serve as a lithmus test for Turkey's democracy and how it views the Kurdish conflict," she said.

The PKK, listed as a terrorist group by Turkey and much of the international community, took up arms for Kurdish self-rule in the southeast in 1984, sparking a conflict that has claimed some 45,000 lives.

Since August last year, the Turkish government has been engaged in a cautious two-pronged strategy of keeping the PKK under military pressure and expanding the cultural and linguistic rights of its Kurdish population in the hope of persuading the rebels to lay down their weapons.

However, an ultimate settlement is not seen as a short-term prospect.

Ankara has already ruled out Kurdish demands for a constitutional recognition of their community as a distinct element of Turkey's population and calls for Kurdish-language education in public schools in the southeast.