Islamist forces are fighting their way into western Syria from bases further east, bringing forward the prospect of US military intervention to stop their advance. If Isis, which styles itself Islamic State, threatens to take all or part of Aleppo, establishing complete dominance over the anti-government rebels, the US may be compelled to act publicly or secretly in concert with President Bashar al-Assad, whom it has been trying to displace.
The US has already covertly assisted the Assad government by passing on intelligence about the exact location of jihadi leaders through the BND, the German intelligence service, a source has told The Independent. This may explain why Syrian aircraft and artillery have been able on occasion to target accurately rebel commanders and headquarters.
Syrian army troops are engaged in a fierce battle to hold Tabqa airbase in Raqqa province, the fall of which would open the way to Hama, Syria’s fourth-largest city.
Further north, Isis has captured crucial territory that brings it close to cutting rebel supply lines between Aleppo and the Turkish border. The caliphate declared by Isis on 29 June already covers the eastern third of Syria in addition to a quarter of Iraq. It stretches from Jalawla, a town 20 miles from Iran, which the Iraqi army and Kurdish Peshmerga are trying to recapture, to towns 30 miles north of Aleppo.