Turkish President Recep Tayyip Erdogan welcomed Russia defense minister, Sergei Shoigu, to Istanbul Sunday to discuss preparations for Syrian civil war “peace talks” also involving Iran and Syrian dictator Bashar al-Assad.

The meeting follows a visit by the U.S. special envoy for the coalition against the Islamic State, Brett McGurk, to Ankara and precedes the first in-person meeting between American President Donald Trump and Russian President Vladimir Putin.

Turkey’s state-run Anadolu Agency reports that Shoigu met with Erdogan and a number of high-ranking Turkish politicians, including “Turkish National Defense Minister Fikri Isik, Chief of General Staff Gen. Hulusi Akar, National Intelligence Organization (MIT) head Hakan Fidan, and Turkish presidential spokesman Ibrahim Kalin.”

While Anadolu did not provide details on the discussion, multiple media outlets suggested the conversation largely focused on the Syrian civil war, which has flooded Turkey with over three million Syrian refugees, according to the United Nations. Anadolu notes that Turkey will be part of multilateral talks with Assad, Iran, and Russia on how to limit the violence in the ongoing civil war. All past iterations of these talks – held in Astana, Kazakhstan – have failed.

The Turkish newspaper Hurriyet notes that Russia and Turkey have supported one another in promoting these talks. “Cooperation between Turkey and Russia has tightened markedly since last year, with the two countries jointly sponsoring peace talks in the Kazakh capital Astana,” the newspaper reports. It adds that Turkey may be seeking to influence these negotiations to the detriment of the Syrian Kurdish People’s Protection Units (YPG), which it considers a terrorist group tied to the Kurdistan Workers’ Party (PKK), a U.S.-designated Marxist terrorist group.

Turkey’s opposition to the YPG’s participation in the war against the Islamic State puts it at odds with both Russia and the United States. The anti-Islamist, leftist-leaning YPG has cooperated with Russia on the ground in operations against ISIS as well as provided ISIS target coordinates for American airstrikes.

In May, the Pentagon announced that it would equip the YPG and its all-female unit, the YPJ, with heavy weapons and praised the group as the only force formidable enough to take on the Islamic State in its “capital,” Raqqa.

On Friday, Erdogan spoke to Putin on the phone, according to Russia news outlet TASS, which cited a Kremlin statement saying Erdogan and Putin “discussed key aspects of the Syrian settlement focusing on the fifth international Astana meeting on Syria, sponsored by Russia, Turkey, and Iran, which is scheduled to be held in early July.”

Putin is expected to have his first in-person meeting with U.S. President Trump this week at the G20 Summit. White House officials have told reporters that “there’s no specific agenda” for the meeting on schedule so far, though tensions in Syria are high on the list of mutual priorities.

On the same day Erdogan spoke to Putin, McGurk arrived to meet Defense and Foreign Ministry officials in Ankara, following a “routine” visit to Syria for updates on the operation to liberate Raqqa. While the details of those conversations remain confidential, that Turkey welcomed McGurk at all is a sign of slightly diminished tensions. Erdogan’s government has previously demanded the U.S. fire McGurk for being too sympathetic to the YPG.

That is not to say the Turkish government has adopted a new attitude towards the Syrian Kurds. On Saturday, Erdogan’s spokesman Ibrahim Kalın did not dismiss the possibility of attacking the YPG considerably in Afrin, near the Turkey-Syria border. “Any threat that may come from Syria or another country towards Turkey – this could be from Daesh, the PYD/YPG, whatever terrorist organization it is – Turkey is responding immediately with all reprisals,” Kalın told reporters.

“It is impossible for us to consent to the support that U.S. provides to the YPG within the context of the Raqqa operation against Daesh terror,” Kalın reiterated.

Turkey deployed troops to Afrin and exchanged fire with the YPG last week, according to various reports from the region. The Kurdish outlet Kurdistan24 claims that Turkey has already begun “preparations… to invade the Kurdish Afrin region in northwestern Syria.”

Rudaw, another Kurdish outlet based in Iraq, reported Friday that all signs pointed to a possible “large-scale conflict” between the Turkish military and the Syrian Kurds.

A YPG commander, Mehmud Berxwedan, threatened that Turkey “will be plunged into a swamp, politically and militarily – there will be an historical resistance against Turkish occupation in Afrin and Shahba regions” if it launches a campaign against the Syrian Kurds.