Iraq, Russia, Iran and Syria have agreed to set up an intelligence committee in Baghdad, a spokesman said Sunday, a further sign of Moscow's growing role in the region's conflict.

Iraq welcomed the creation of the new cell as a chance to help harmonize often competing efforts in the fight against the Islamic State (IS) jihadist group.

Russian President Vladimir Putin spoke to Saudi Arabia's King Salman about finding a solution to the Syria crisis on Saturday, just two days before he is due to address the U.N. on the issue, the Kremlin said.

In a telephone conversation at Russia's behest, the two men "exchanged views on regional security matters, first and foremost, in the context of finding ways to settle the conflict in Syria", a statement posted to the Kremlin's website said.

Russia on Saturday freed Estonian officer Eston Kohver jailed for spying last month, exchanging him for a Russian spy in a Cold War-style bridge swap just days before President Vladimir Putin's visit to the United Nations.

Kohver, who was sentenced in August to 15 years in jail on espionage and other charges, was exchanged for Aleksei Dressen, a former Estonian security official serving a 16-year sentence for spying for Moscow, the FSB security service said in a statement.

Russia kept up its military buildup in Syria on Saturday with a fresh transport flight into a new airbase in the heartland of its regime ally, a Syrian military source told Agence France Presse.

It was the 15th straight day that a Russian transport aircraft had flown in troops and equipment to the Hmeimim base in Latakia province on the Mediterranean coast, the source said on condition of anonymity.

Russia agreed to resume gas supplies to Ukraine over the winter under a deal clinched late Friday with the European Union, capping months of difficult talks overshadowed by the Ukrainian conflict.

European Commission vice president for energy, Maros Sefcovic, told a press conference the preliminary deal was a "crucial step" to ensure Ukraine has gas supplies from October through March and that Europe receives onward deliveries. 

Russia has shocked the West by boosting its military presence in Syria as President Vladimir Putin seeks to not just defeat Islamic State radicals but also to gain a firm foothold in the strategic Middle Eastern country.

Putin has seized the initiative more than four years into a civil war that has killed more than 240,000 people and led to the emergence of IS, amid the collective failure of the international community to stop the violence.

Russia's President Vladimir Putin said the only way to end the war in Syria is to support its existing government in the fight against terrorism, in remarks released Thursday.

In an interview with CBS News "60 Minutes," the Russia leader repeated his view that only the Syrian people can decide if and when to replace President Bashar Assad.

The United States and Russia could find ways to cooperate on the crisis in Syria, Pentagon chief Ashton Carter said Thursday, as Moscow continues a military build-up in the war-torn nation.

Carter said if Russia were to pursue a political solution to the four-and-a-half-year Syrian crisis, and not just "indiscriminately" attack foes of President Bashar Assad, "we could find areas of cooperation."

Russian President Vladimir Putin said Americans should not think of him as an autocratic "czar" and praised their openness and creativity, in an interview ahead of a trip to New York.

Putin is to meet U.S. President Barack Obama next week on the sidelines of the UN General Assembly, amid renewed East-West tensions after Russia's interventions in Ukraine and Syria. 

Russia's President Vladimir Putin will meet U.S. leader Barack Obama during his visit to the UN in New York on Monday, as the U.S. frets about a military buildup by Moscow in Syria.

Kremlin spokesman Dmitry Peskov confirmed to Russian news wires that the meeting will go ahead after the two leaders address the United Nations General Assembly.