The Islamic State group consolidated it’s control of the Iraq-Syria border Friday after capturing an Iraqi, provincial capital and a famed Syrian heritage site in an offensive that has forced a review of US strategy. The jihadists, who now control roughly half of Syria, reinforced their self declared transfrontier “caliphate” by seizing Syria’s Al-Tanaf crossing on the Damascus-Baghdad highway late Thursday. The jihadists surge, which has also seen it take Anbar capital Ramadi and the ancient Syrian city of Palmyra in the past week, comes despite eight months of US-led air strikes. It has sparked an exodus of tens of thousands of civilians in both countries and raised fears IS will repeat at Palmyra the destruction it had already wreaked at ancient sites in Iraq’s Nimrud and Mosul. The United Nations said Friday at least 55,000 people had fled Ramadi alone since mid-May. President Barack Obama has played down the IS advance as a tactical “setback” and denied the US-led coalition was “losing” to IS. But French President François Hollande said the world must act to stop the extremists.