Bloodshed has in the past marred Newroz day, March 21, which the Kurds use as a platform to demand greater freedoms or demonstrate support for the separatist Kurdistan Workers' Party (PKK), which has beeen fighting the army since 1984.

The Kurdish conflict, which has claimed more than 37,000 lives, has long hampered Turkey's bid to join the European Union and continues to cast a pall on its commitment to democracy and human rights.

The police headquarters in Ankara warned Friday over possible attempts by Kurdish separatists "to stage provocative acts of mass violence" at Newroz, Anatolia news agency reported.

"We expect our people to remain calm in the face of such acts... and respect the law," police spokesman Ismail Caliskan said.

Even though celebrations have been relatively peaceful in recent years, officials fear Kurdish radicals could use this year's festivities to stir unrest as part of the PKK's renewed armed campaign in the southeast, marked also by a series of bomb attacks on civilian targets blamed on the group.

Tension in the region has also escalated over the November bombing of a Kurdish-owned bookstore in the town of Semdinli, which two soldiers and a Kurdish informer are accused of perpetrating.

The incident sparked deadly riots and accusations that Ankara has failed to purge rogue elements in the security forces accused of summary executions, extortion, kidnappings and drug-smuggling in the 1990s, when the PKK campaign in the region was at its peak.

As the PKK called on Kurds to step up their "uprising" during Newroz, Kurdish politicians and civic groups appealed for calm and urged the population to stay away from "provocations."

"Everyone should fulfil their responsibilities so that the people can celebrate the Newroz in a free atmosphere," said Osman Baydemir, the Kurdish mayor of Diyarbakir, the main city of the southeast.

Traditionally, Diyarbakir serves as the venue for the biggest Newroz festivities, which each year draw at least 50,000 people from the region.

The PKK has denounced the relatively peaceful atmosphere in Diyarbakir in recent months and urged residents to "shake off their lethargy" on Newroz, which traditionally marks the arrival of spring.

"Do not yield to the intoxicating and deadly spirit of festivals and cultural events," the statement said. "Step up and radicalize the uprising!"

The interior ministry has ordered police across the country to block any attempts to turn Newroz celebrations into pro-PKK demonstrations and not to tolerate PKK flags and slogans praising the group.

Keen to improve their image in EU eyes, Turkish police in recent years often tolerated open support for the PKK, blacklisted as a terrorist group by Ankara, the EU and the United States.

In the bloodiest Newroz so far, about 50 people were killed by security forces in 1992 during clashes across the southeast.

More recently, two men were crushed to death and dozens injured in a police clampdown on violent Newroz demonstrations in 2002 in the Mediterranean port of Mersin, home to particularly militant migrant Kurds although not in a traditionally Kurdish-populated area.

Newroz, which marks the awakening of nature at the March 21 equinox, is also celebrated in Iran and other Muslim communities in the Caucasus and Central Asia.