Images of smoke plumes rising over the Iraqi desert as troops move to liberate Mosul from ISIS may seem very far removed from life in Europe. But the turmoil could spill into the continent as the offensive puts both refugees and foreign jihadists on the move, and strains delicate relations with Turkey. The most urgent concern for Europe – voiced this week by French President François Hollande – is the presence of around 4,000 Europeans fighting with extremists in Iraq and Syria.