Islamic State militants have shot down an Iraqi military helicopter, officials said yesterday, killing the two pilots and raising fresh concerns about the extremists' ability to attack aircraft amid ongoing US-led coalition airstrikes.

The attack happened in the Shi'ite holy city of Samarra, about 60 miles north of Baghdad.

A senior Defence Ministry official said the Sunni militants used a shoulder-fired rocket launcher to shoot down the EC635 helicopter on the outskirts of the city. International airlines changed their commercial flight plans over the summer to avoid Iraqi air space.