Ankara (AFP) - 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 suggesting Kurds should push for autonomy in their stronghold of the southeast of the country.

"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.

The charismatic 42-year-old Demirtas 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."

- 'Puppets of terror?' -

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."

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."

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.

Story continues

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.

The military confirmed the death of the child, but said the boy had been killed by PKK fire.

Last week, a three-month-old baby and her grandfather were killed when they became caught in the crossfire, again in Cizre.

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

- Police disperse protest -

In the mainly Kurdish city of Diyarbakir, police fired tear gas and water cannon against protesters who demonstrated against the curfew in the Sur district of the city, an AFP photographer said.

Nearly 2,000 protesters made up of representatives from left-wing unions gathered outside the city's municipality but police blocked them from staging a march.

Then almost 300 protesters from the group attempted to occupy a major street but were dispersed by the police who responded with tear gas and water cannons.

And 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 provinces of Sirnak and 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.