The fight to liberate the Syrian city of Raqqa, the self-proclaimed "capital" of ISIS, is a perfect lesson in the bewildering complexities of the Middle East: Everyone wants the Raqqa offensive against the terrorist organisation to succeed but, for most of the region's governments, who does the fighting is just as important as the outcome.

The assault is being spearheaded by the Syrian Democratic Forces (SDF), a 30,000-strong unit created by the United States a year ago to chase out the Islamic State in Iraq and Syria and topple the government of Syrian President Bashar al-Assad.

The rebels, boosted by the presence of the US special forces, have been successful. Their pincer movement on Raqqa is well-timed, coming just as Iraqi forces are besieging Mosul; if the two cities are liberated, ISIS will be largely obliterated.

Awkwardly, however, the SDF is dominated by offshoots of the Kurdistan Workers' Party (PKK), an ethnic Kurdish force which has fomented separatist violence in neighbouring Turkey for decades. Turkey is furious that the PKK - itself classified as a terrorist group - is now being used by the Americans to fight another terrorist organisation. But Washington says these are exceptional circumstances.

General Joseph Dunford, the chairman of the US Joint Chiefs of Staff, is in Turkey trying to reassure President Recep Tayyip Erdogan that the Kurds will not be in the forefront of Raqqa's liberation, but will merely be used to tighten the noose around the city. Yet the Turks are pushing instead their own troops inside Syria to create a buffer zone against the Kurds.

It will be a bitter irony if the eventual liberation of Raqqa and the defeat of ISIS is followed by a breakdown of the alliance between Turkey and the US, which remains crucial to the handling of Syria.

However, that is now a real danger - the Americans have to prevail in Raqqa and also ensure their victory is not followed by strategic disarray.

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