Russian President Vladimir Putin, right, and his Turkish counterpart Recep Tayyip Erdogan at Putin’s residence in the Russian Black Sea resort of Sochi, Russia, on May 3, 2017. (Alexander Zemlianichenko/AP)

Russian President Vladimir Putin expanded a diplomatic blitz over the war in Syria on Wednesday, meeting with Turkey’s president as the Kremlin pushes a proposal to create “deconfliction zones” in Syria with what Putin said was U.S. support.

The talks with Turkish Prime Minister Recep Tayyip Erdogan reflect possible growing cooperation between nations once deeply at odds over Syria’s conflict — with Turkey backing rebel factions and Russia providing key military support to Syria’s government.

Turkey would have an important role in any bid to create safe areas in Syria for opposition groups and Syrians displaced by more than six years of fighting. But its description of the zones appeared to differ somewhat from Russia’s, and President Trump has not yet spelled out what the United States has in mind.

The Putin-Erdogan talks in the Black Sea resort of Sochi followed a flurry of discussions between Putin and Western leaders, including a visit by German Chancellor Angela Merkel to Sochi on Tuesday, and what was Putin’s first talk with Trump since last month’s U.S. strike on a Syrian air base. The White House said without elaboration that the leaders had discussed “safe, or de-escalation, zones . . . for humanitarian and many other reasons.”

In a news conference with Erdogan, Putin said he supported the creation of the safe zones — in which he said “aircraft will not operate” — in an effort to support a Syrian cease-fire. Putin said his talks with Trump suggested “the U.S. administration support them as well.”

But Syrian rebel groups refused to attend a Wednesday session of cease-fire talks in Kazakhstan, citing continued bombing of rebel-held areas despite a cease-fire agreed early this year by Russia, Iran and Turkey. It was not immediately clear whether they would return to the negotiations.

U.N. Syria envoy Staffan de Mistura, speaking outside the talks in Astana, the Kazakh capital, said “the United Nations is very concerned at the reports of escalation in Syria, including, allegedly, reports of airstrikes,” especially while “proposals to de-escalate the conflict are under very serious discussion.”

Only Russia and Syria operate aircraft in the civil war; Russia has insisted that its planes are not involved.

Trump advocated “safe zones” throughout his presidential campaign but did not define them. On at least two occasions in March, Secretary of State Rex Tillerson publicly referred to “zones of stability” as areas cleared of the Islamic State to which former residents could return.

Asked Wednesday to elaborate on Trump’s discussion of “de-escalation, or safe zones” this week with Putin, Air Force Col. John Dorrian, spokesman for the Baghdad-based anti-Islamic State coalition said, “I’m afraid I can’t do that, because it would be speculation on my part if I did.” While he was aware of the Putin-Trump conversation, Dorrian said, “I don’t have any insight on what the discussions were beyond the fact that they happened.”

Other U.S. officials indicated that the White House reference was to the need for a durable cease-fire that would allow the delivery of humanitarian aid and eliminate what has been a major distraction in the U.S.-led coalition campaign against the Islamic State in Syria.

Turkey advocated for the creation of no-flight zones early in the Syrian war as tens of thousands of refugees fled the fighting, crossing the border into Turkish territory, and as Erdogan emerged as one of the region’s foremost backers of the rebellion against Syrian President Bashar al-Assad. More recently, the Turkish government has viewed “safe zones” in northern Syria as a bulwark against expansion by Syrian Kurdish fighters, allied with the United States in the fight against the Islamic State, who now control much of the border.

Turkey sent its military into Syria last year to fight against the militants as well as to check the expansion of Kurdish forces. It now refers to the area it captured as a de facto safe zone.

According to a copy of a Russian proposal presented to rebel leaders in Astana, the Kremlin proposed the creation of four “de-escalation zones” in Syria that would prevent direct clashes between rebel and government forces. Three of the four — the northwest province of Idlib; the Damascus suburb of East Ghouta; and southwestern Syria near Jordan and the Golan Heights — have been sites of recent bombings allegedly by the government. The fourth area is north of the city of Homs, in west-central Syria.

According to the document, Russia proposed that “the use of any kind of weapon in the de-escalation zones by the parties to the conflict shall be prohibited, including the planes of the Syrian armed forces.” Other versions, published in Arabic-language media, did not include the stipulation about government aircraft.

The Islamic State and al-Qaeda’s Syrian affiliate would be excluded from the cease-fire. In the past, Russia and Syria have carried out airstrikes in rebel and civilian areas, saying they were targeting terrorists.

DeYoung reported from Washington. Kareem Fahim and Louisa Loveluck in Istanbul contributed to this report.