ANKARA : Turkish President Recep Tayyip Erdogan on Tuesday accused the leader of the main Kurdish party Selahattin Demirtas of "treason" over his call for autonomy for the country's Kurdish minority.

In a speech at the weekend, Peoples' Democratic Party (HDP) co-chairman Demirtas said that Turkey's largest ethnic minority had to decide whether to live in autonomy or "under one man's tyranny".

On Monday, prosecutors opened a criminal investigation against him for crimes against the constitutional order over the remarks.

"What the co-leader has done is clearly provocation, treason," Erdogan told reporters Tuesday at Istanbul airport before leaving for Saudi Arabia. "This is the time when the masks have been taken off and the real faces exposed," he said.

"How dare you talk about establishing a state in the southeast and in the east within Turkey's existing unitary structure," he said, addressing Demirtas. "You cannot take such a step. Neither the national will, nor our security forces, armed forces, police, village guards will allow such a thing."

The charismatic 42-year-old has emerged as Erdogan's key rival over the last year, with many commentators saying he is the only politician to rival the Turkish strongman's rhetorical skills.

Under party rules Demirtas shares the leadership of the HDP with a woman, Figen Yuksekdag.

In an address to HDP lawmakers in the parliament, Yuksekdag hit back, saying: "If there is a word to describe us, it's not treacherous but loyal. We are loyal to our peoples' struggle."

The Turkish government labels the HDP a political front for the militant Kurdistan Workers' Party (PKK) which is designated as a terrorist organisation by Ankara and its Western allies.

Erdogan accused HDP politicians of being "puppets of the terrorist organisation." "The will of the people is stronger than arms," the president said. "They have no faith in the parliament."

Referring to the criminal investigation against Demirtas, Erdogan said: "I believe that the treachery network dealing a blow to our country's unity will learn a lesson it deserves from our people and from the law."

Prime Minister Ahmet Davutoglu had cancelled a scheduled meeting with Demirtas planned this week to discuss constitutional reforms, chastising the party for banking on "conflict and tensions."

The HDP's Yuksekdag said: "You are turning the tables and cancelling the meeting. Where and how will the constitution be discussed?"

Tensions are running high in Turkey's predominantly Kurdish southeast, which has been rocked by curfews imposed on several towns where the security forces have been battling PKK militants.

A five-year-old boy, named as Huseyin Selcuk, was shot dead this week while playing in the garden at his home in the flashpoint town of Cizre, local media reported.

Last week, a three-month-old baby and her grandfather were killed when they became caught in the crossfire between security forces and Kurdish rebels, again in Cizre. The baby was hit in the head when the family's house was shelled during clashes.

Residents of the towns under curfew are facing food shortages and problems with water and electricity supplies. Many homes have been damaged by shelling.

In Ankara, around 700 protesters congregated in Sakarya Square, demanding peace, an AFP photographer reported.

The group unfurled banners: "No to war. Peace now!" and "No to policies of war and pressure."

The army says more than 200 PKK militants had been killed in the current campaign in the southeast which started earlier this month, including the province of Sirnak and in the mainly Kurdish city of Diyarbakir.

Yuksekdag said 360 civilians, including 61 children and 73 women, had lost their lives since the violence erupted this summer.

It is not possible to independently verify the figures and the areas remain under army curfew with access barred to outside observers.