Bashar al-Assad’s troops are on a collision course with Western special forces, after advancing towards their training base in eastern Syria over the weekend.

Pro-government soldiers are now within 15 miles of al-Tanf - a heavily fortified hub for American and British special forces training Syrian rebel groups, which are fighting Islamic State of Iraq and the Levant (Isil) near the Iraqi border.

The assault is being led by Iranian forces, which are commanding Syrian troops and a number of Lebanese Hizbollah fighters with the help of Russian jets in the skies.

The Syrian army has been alarmed by two months of Free Syrian Army (FSA) advances against Isil that allowed the rebels to secure a large swathe of sparsely populated territory stretching from south east of Damascus all the way to the borders with Iraq and Jordan.

Syrian forces have in recent days moved tanks and surface-to-air missiles closer to the eastern frontline with the moderate FSA units in an apparent warning to the US-led coalition, which flies sorties against Isil in the area.