The SDF meanwhile controls most territory east of the River Euphrates, including the city of Raqqa. Until 2017, it was the de facto capital of the "caliphate" proclaimed by IS, which now controls only a few pockets across Syria.

Will the war ever end?

Image copyrightAFP

It does not look like it will any time soon but everyone agrees a political solution is required.

The UN Security Council has called for the implementation of the 2012 Geneva Communique, which envisages a transitional governing body "formed on the basis of mutual consent."

But nine rounds of UN-mediated peace talks - known as the Geneva II process - since 2014 have shown little progress.

President Assad has appeared increasingly unwilling to negotiate with the opposition. The rebels still insist he must step down as part of any settlement.

Meanwhile, Western powers have accused Russia of undermining the peace talks by setting up a parallel political process.

The so-called Astana process saw Russia host a "Congress of National Dialogue" in January 2018. However, most opposition representatives refused to attend.