The largest crowd was expected in Diyarbakir, the central city of the mainly Kurdish southeast, where the Newroz celebrations, marking the arrival of spring and the Kurdish New Year, have been mired in bloodshed in the past.

Newroz Day has become a platform for the Kurdish minority to demand greater freedoms or demonstrate support for the Kurdistan Workers' Party (PKK), which has beeen fighting for self-rule in the southeast since 1984 and is listed as a a terrorist group by Ankara and much of the international community.

President Ahmet Necdet Sezer called on Kurds to "act with common sense, stay away from provocations ... and deny any opportunity to those who aim at separatism."

In Diyarbakir, hundreds of police officers, some in armoured vehicles, were deployed at the venue of the festivities and searched revellers before allowing them in.

The festivities were organised by Turkey's main Kurdish political movement, the Democratic Society Party (DTP), whose members have increasingly become the target of judicial action for backing the PKK in recent weeks.

In Ankara, Prime Minister Recep Tayyip Erdogan issued an appeal for peace and unity at official Newroz ceremonies, which the government has begun holding in recent years in a bid to prevent the day from being monopolised by Kurdish militants.

"Let the seeds of hatred and hostility burn in the bonfires," Erdogan said. "As long as we do not break each other's hearts, no one can damage our unity."

He then set alight a traditional Newroz bonfire and several of his ministers took turns to jump over it.

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

Celebrations in Turkey have been relatively calm in recent years, but the police in Istanbul and nearby Kocaeli detained last week 12 suspected Kurdish rebels in possession of 11.7 kilograms (25.7 pounds) of plastic explosives, reportedly intended for bomb attacks at Newroz.

The run-up to the festival was also marred by allegations that jailed PKK leader Abdullah Ocalan is being gradually poisoned with toxic substances in the northwestern island of Imrali, where he is the sole prisoner.

Ankara rejected the accusations, made by Ocalan's lawyers in Rome on March 1, but the DTP warned of Kurdish violence "if something bad happens" to the rebel chieftain, whom many Kurds uphold as a national hero and freedom fighter.

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 in a police clampdown on violent Newroz demonstrations in 2002 in the Mediterranean port of Mersin, home to a particularly militant community of migrant Kurds.

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.

Under EU pressure, Ankara has in recent years broadened Kurdish cultural freedoms, but Kurdish activists say the reforms are inadequate and have called on the government for a general amnesty for PKK militants to encourage them to end their armed struggle.