Pentagon Press Secretary Rear Admiral John Kirby tweeted: "US military aircraft conduct strike on Isil [Islamic State] artillery. Artillery was used against Kurdish forces defending Erbil, near US personnel."

Two F-18 fighters dropped laser-guided 500-pound bombs on the mobile artillery target. Militants of the Islamic State were using artillery that has been abandoned by the Iraqi army when it fled to shell Kurdish forces defending the regional capital of Kurdistan.

US airstrikes were very small and very targeted and the Peshmerga Kurdistan forces are waiting for more strikes by the US fighter jets, according to reports.

Kirby said that the decision to strike "was made by the US Central Command commander under authorisation granted him by the commander in chief". The strikes took place at 6.45am EDT (10.45 GMT).