US President

Unifying Syria is an extremely difficult proposition, with the country currently divided between forces loyal to Kremlin-allied strongman Bashar al-Assad, the US-backed Syrian Democratic Forces (SDF) and several jihadist groups and rebel units.

The two presidents emphasized the need to implement UN Security Council Resolution 2254, which calls for a ceasefire and humanitarian access as part of efforts to end the conflict, and UN-led peace talks in Geneva, the White House said in a statement.

The aim is "to peacefully resolve the Syrian civil war, end the humanitarian crisis, allow displaced Syrians to return home and ensure the stability of a unified Syria free of malign intervention and terrorist safe havens," it said.

The United States has backed various rebel forces in Syria as well as the SDF, which has battled the Islamic State jihadist group, while Russia is an even more active party to the conflict, carrying out air strikes directly in support of Assad's forces.

Anti-government protests broke out in Syria in 2011, and the government's brutal response sparked a civil war that has wracked swathes of the country.