About a fortnight ago, Dr Tareq Kamleh was revealed to be working for ISIS when a video was released in which Kamleh encouraged other Muslim health professionals to travel to Syria.

In a letter from the Adelaide-trained doctor, obtained by the Sunday Mail, he denies being recruited by ISIS, and says his decision to join the group was "very well educated and calculated... it did not involve any brainwashing."

In the letter, Kamleh was highly critical of Australia and the coalition forces fighting against ISIS.

"Interestingly the two drone strikes that have occurred since I have been here have not claimed the life of a single male, let alone a soldier. Good work 'Team Australia'," he wrote. "From what I've seen you have more blood on your hands than ISIS has on their knives."

The Sunday Mail reports the letter was also sent to the Australian Health Practitioner Regulation Agency.