Russia and the United States will continue their efforts fighting against the Islamic State of Iraq and the Levant (ISIL) group in Syria, US President Donald Trump and Russian Vladimir Putin have agreed.

In a joint statement released by the Kremlin and issued on the sidelines of an Asia-Pacific summit in Vietnam on Saturday, the leaders agreed there was no military solution to the conflict in Syria and called on all parties to take part in the Geneva process.

The White House did not immediately confirm the details of the statement.

Syria's Bashar al-Assad's commitment to the process, in line with a UN Security Council resolution, implies "constitutional reform and free and fair elections under the supervision of the United Nations" in which all Syrians can participate, the statement further said.

Local Russian media also reported that the two parties promised to maintain existing Russian-US military channels of communication to ensure the security of the armed forces.

Russia has been the Syrian government's main ally in the six-year civil war, while the US has been backing the Syrian Kurdish rebels on the ground since 2014.

The US has led a coalition carrying out air raids against ISIL, also known as ISIS, in Syria.

The armed group has been pushed from its main strongholds in recent months by the Syrian army and the US-backed Kurdish and Arab coalition.

Trump and Putin also confirmed their support for de-escalation zones in Syria, including one in the southwest that the presidents agreed to at a meeting in July in Germany.

They also called on UN members to increase humanitarian aid contributions for Syria.

Although a meeting between Trump and Putin was widely expected at the APEC summit, the Kremlin statement did not confirm details of their talk.