“We need to use our diplomatic and more traditional intelligence assets to bring pressure on the governments of Qatar and Saudi Arabia, which are providing clandestine financial and logistic support to Isil and other radical Sunni groups in the region,” Ms Clinton wrote.

Mr Assange noted the US government had never acknowledged governments of Middle East nations had financially supported Isis, instead arguing such support was isolated to “some rogue princes using their cut of the oil money to do whatever they like, although the government disapproves”, according to the WikiLeaks founder.