By Diyar Guldogan

SOCHI, Russia

Ankara, Moscow and Tehran have agreed to hold the Syrian National Dialogue Congress, Turkey's President Recep Tayyip Erdogan said on Wednesday.

"We hope that this fruitful cooperation between our countries will have a positive effect on the whole region and reduce tensions and the risk of sectarian disintegration in the region," Erdogan said at a joint news conference with his Russian and Iranian counterpart.

Erdogan, Vladimir Putin and Hassan Rouhani met in Russia's Black Sea city of Sochi to discuss progress made in the Astana peace talks and changes in de-escalation zones across Syria.

The zones were established to reinforce a ceasefire introduced by the three guarantor states last December.

Erdogan said the three countries supported the territorial integrity and sovereignty of Syria.

He added Turkey, Russia and Iran had reached a consensus on an "inclusive and fair" political transition process in Syria.

However, Erdogan warned that Turkey cannot share a platform with any terrorist organization that poses a threat to its national security.

"Exclusion of terrorist elements -- that target both Syrian political union and territorial integrity and our country -- from the process, will be among our priorities as Turkey," he added.

Ankara reiterated there is no difference between the PKK, YPG and PYD terrorist organizations.

The PYD and its military YPG wing are Syrian branches of the PKK, which has waged war against Turkey for more than 30 years.

Since the PKK launched its terror campaign in Turkey in 1984, tens of thousands of people have been killed.

"If we are committed to the territorial integrity and political unity of Syria, we can not perceive a blood shedding gang, who wants to divide this country, as a legitimate actor," Erdogan said.

Putin confirmed the three leaders had agreed to hold congress in Sochi.

"I would like to express my gratitude to the Turkish and Iranian leaders for welcoming the idea of holding the Syrian National Dialogue Congress regarding the solution of the Syrian crisis," he said.

He said the countries' foreign and defense ministries were given instructions about its structure.

Putin added that the leaders had discussed socio-economic reform for Syria.

Rouhani reiterated his commitment to hold the congress.

He said it was an "important" meeting that had prepared grounds for the formation of peace and stability in Syria.

"The aim is that at the National Dialogue Congress, all active parties, against Syria and even those who are in favor of the regime, will come together to negotiate the future of the country," Rouhani said.

Putin later hosted a dinner for Erdogan and Rouhani.

Syria has been locked in a vicious civil war since 2011, when the Bashar al-Assad regime cracked down on pro-democracy protests with unexpected ferocity. Since then, hundreds of thousands of people have been killed in the conflict, according to the UN.