With the integration process into the EU... we are not expecting the Turkish authorities to close us

Hadep official Sunullah Altan

Thousands of supporters have gathered to take part in the congress, which takes place as the party waits for a court decision on whether it will be banned.

Hadep supporters say they are confident that Turkey's hopes of joining the European Union will discourage the authorities from imposing a ban, which would almost certainly incur EU criticism.

The government has often dismissed Hadep as the political wing of the illegal PKK rebel movement but it remains by far the most popular party in the predominantly Kurdish south-east of the country.

Police intervention

Hadep said that paramilitary police had prevented hundreds of Kurdish activists from travelling to Ankara for the congress.

Hadep is calling for greater cultural rights for ethnic Kurds

A statement said at least 35 people were detained near the south-eastern town of Semdinli.

It said that dozens of cars and buses were stopped in the south-eastern provinces of Hakkari and Siirt and the eastern province of Van and ordered back to their home towns.

The party's future currently hangs in the balance, as the constitutional court considers whether it should be closed down for illegal activities.

"With the integration process into the EU... we are not expecting the Turkish authorities to close us. But this is the fourth party we've had and we're used to being closed down," Sunullah Altan, a party official from Istanbul, told Reuters news agency.

Cultural rights

Hadep argues that it has never advocated violence and is simply trying to represent the views of its supporters.

Hadep pursues many of the same goals as Ocalan

There is no doubt that it is pursuing many of the same goals as the PKK and its leader Abdullah Ocalan, but Hadep officials deny that there is any organic link.

The party is campaigning for greater cultural rights for millions of ethnic Kurds in Turkey but it says it poses no threat to the country's territorial integrity.

Last year Hadep won real political power for the first time.

It took control of municipal government in several towns and cities in the south-east, despite constant harassment from the police during the election campaign.

Changing attitudes

The BBC's Chris Morris in Ankara says there is still a high level of official distrust of Hadep, but there are also hints that attitudes may slowly be changing.

A lot hinges on the decision of the constitutional court and no one knows exactly when a ruling might come.

Hadep points out that even if it were to be banned another party would quickly be formed to campaign on the same issues.

Our correspondent says party leaders hope that both the government and the military leadership in Ankara will begin to accept greater diversity in political life as part of a broader process of reform.

But that is a debate which is far from over.