Turkish President Recep Tayyip Erdogan has accused the leader of the pro-Kurdish Peoples' Democratic Party (HDP) of betrayal by calling for autonomy in the south-east of the country.
Erdogan told journalists on Tuesday in Istanbul that Selahattin Demirtas' comments Sunday on autonomy for Kurds in south-eastern Turkey were a "clear provocation."
"How dare you talk about establishing a state in the south-east and the east within Turkey's existing unitary structure?" state news agency Anadolu quoted Erdogan as saying.
"You cannot take such a step. Neither this country's national resolve nor our security forces will allow such a thing," the president said at Ataturk Airport before flying to Saudi Arabia.
According to Anadolu, the Ankara prosecutor's office Monday said it had launched an investigation against Demirtas for his remarks calling for the formation of "democratic autonomous regions" in the south-east.
Five others - including well-known HDP lawmaker Sirri Sureyya Onder - were also to be investigated for their comments at the meeting of Kurdish groups in the south-eastern city of Diyarbakir, Anadolu reported.
Among the accusations against them are "terrorist propaganda" and "disrupting the unity and territorial integrity of the state."
HDP sources said they had no information on the investigation.
Meanwhile, Turkish trade unions were demonstrating on Tuesday in Diyarbakir against curfews being imposed in the south-east, particularly in the district of Sur.
Some 2,000 members of unions critical of the government quit work and gathered in the centre of the city, news agency DHA reported. While most of them dispersed after their sit-in, some 300 demonstrators clashed with police. Security forces used tear gas and water cannon against them.
Strict around-the-clock curfews have been imposed on residents of Kurdish areas, raising resentment among locals, since early December.
International rights groups have sharply criticized the curfews, saying that they punish the entire population, and locals have no access to food and water.
Scores of militants of the banned Kurdistan Workers' Party (PKK) have been killed in recent days as the Turkish military launched a fresh offensive in the south-east.
Turkey has deployed tanks and helicopters as it steps up its attacks, largely focused on four provinces, following five months of violence between the government and Kurdish militants.
The PKK and the government have been at war since 1984, leaving more than 40,000 people dead. Peace talks collapsed this year and a two-year ceasefire broke down in July.
The Kurdish minority, which comprises at least 15 per cent of the population, has long complained of systemic discrimination.