A Turkish military tank advances on a street in Afrin, Syria, on March 24, 2018. (Xinhua)

ANKARA, March 25 (Xinhua) -- The presidents of Turkey, Russia and Iran will meet in a trilateral summit on Syria in Istanbul on April 4.

It comes after the capture by Turkish-led forces of a Kurdish stronghold in northern Syria and amid Turkish threats to extend the massive operation further east.

The meeting will be hosted by Turkish President Recep Tayyip Erdogan and will be the second such tripartite summit following the previous one last November in the Russian Black Sea resort of Sochi.

The summit will be attended by Russian President Vladimir Putin and his Iranian counterpart Hassan Rouhani as the three leaders will seek to salvage their efforts to end the seven-year Syrian conflict.

As part of peace talks in the Kazakh capital Astana sponsored by Ankara, Moscow and Tehran, the three countries' foreign ministers met on Friday and discussed preparations for next month's summit, the Turkish foreign ministry said in a statement.

The three countries have worked together despite their different positions. While Iran and Russia have provided military support to the regime of Syrian President Bashar al-Assad, Turkey has repeatedly called for his ousting and supported Syrian rebels.

MESSAGE OF COOPERATION

Experts believed that the mere fact that regional actors are gathering would be considered as a message of international dialogue in search of a negotiated peace in war-torn Syria.

"The most concrete result that would emerge from this summit will be one of the determination to pursue the cooperation between Turkey, Russia and Iran," said Kerim Has, a lecturer at Moscow State University.

The specialist on foreign relations and Russia commented that "such a message despite the Afrin operation would be important for the three (regional) players."

He was referring to the offensive launched by Turkish troops against Kurdish fighters in the Syrian enclave.

Ankara on Jan. 20 launched an air and ground offensive with Syrian rebels against the Syrian Kurdish People's Protection Units (YPG) militia that Ankara considers as a terrorist group in Afrin in northern Syria.

The main objective is to cleanse the Kurdish forces from its 900-km-long border with Syria, victim of a civil war for seven years.

The operation, dubbed Olive Branch, follows Turkey's 2016-2017 offensive Euphrates Shield in Syria against the YPG and the Islamic State (IS) extremist group.

TURKEY VOWS TO EXTEND OPERATIONS

Turkish-led forces captured virtually unopposed Afrin city center nearly two months into the incursion. Erdogan has vowed to expand the offensive to other Kurdish-held regions further east, sparking fears of a possible clash with U.S. troops deployed in the area.

"We will continue this process until we entirely eliminate this corridor, including in Manbij, Ayn al-Arab and Tal Abyad," the Turkish leader said, insisting also that when the "security threat for Turkey is eliminated, we will not be indefinitely there, we will retreat."

Assurances given by the Turkish leadership that Turkish troops will not stay in Syria are essential for the implementation of ground rules covered by the Astana and Geneva agreements and their signatories, reminded Has.

"It would be appropriate to consider the military and political outcome of the Afrin operation on a short and medium term ... The other actors would certainly not welcome the creation of a zone under Turkish sovereignty on Syrian soil," he added.

As part of the Astana process, Turkey, Iran and Russia have set out to create four so-called de-escalation zones in Idlib, the greater Damascus area, the southern region of Daraa and the city of Homs.

But intense bombardment has hit in recent weeks Eastern Ghouta, a rebel enclave near Damascus, designated in May 2017 as a "de-escalation zone," killing hundreds of civilian, according to independent sources.

"The deplorable situation in Eastern Ghouta will be on the table" in Istanbul, said a Turkish diplomatic source to Xinhua on condition of anonymity.

The Istanbul summit will also be the latest example of the intensifying dialogue between Ankara and Moscow on the Syrian crisis.

The two countries have been working closely together since a 2016 reconciliation deal ended a crisis sparked by the downing by Turkey of a Russian war plane over Syria.

Turkey saw its bilateral relations with NATO ally the United States faltering over its military support for the YPG, who has helped the U.S.-led coalition in its fight against the IS since 2014.

Erdogan on Tuesday criticized the U.S. for not having sided with Turkey's security concerns in Syria. "You say you are our strategic partner, and then you go and collaborate with terrorists," he said, referring to the Kurdish militia, calling on Washington to "respect" Turkey.

Washington announced on Tuesday a plan to eject the YPG from Manbij, which Turkey denied having been approved by the United States, raising fears that the two NATO partners could dangerously confront each other in this area where 2,000 U.S. special forces are stationed.

Some analysts thought that by giving a green light to Turkish airplanes to use the space it controls over Syria, Russia has meddled in the Turkish-U.S. dispute to weaken the NATO alliance.

"The green light given to Operation Olive Branch shows that even though they are reluctant, Russia and Iran prefer Turkey who would transfer in the end the control of Afrin to regime forces rather to an independently manoeuvring YPG, who would be unpredictable," argued Has.

The fact that Turkey has promised to rebuild the infrastructure of Afrin and ensure the safe return of thousands of refugees is also a factor that justifies Ankara's motive.

While the U.S. State department spokesperson Heather Nauert has voiced concern over a mass evacuation of Afrin city, quoting the United Nations reporting up to 250,000 Kurds having fled the region, massive preparations are underway by Turkish aid organizations such as the Red Crescent to provide immediate assistance to the population of Afrin, said Turkish Deputy Prime Minister Bekir Bozdag on Tuesday.

"We want to make sure that our operation brings hope to all ethnic populations of Afrin," said the Turkish diplomatic source, implying that until the trilateral summit of April serious assistance will be conveyed to this part of Syria.