Is magnetic field due to an electric current a relativistic effect?

Several authors have asserted that the magnetic field due to an electric current is a relativistic effect. This assertion is based on the fact that if one assumes that the interaction between electric charges is entirely due to the electric field, then the relativistic force transformation equations make it imperative that a second field - the magnetic field - is present when the charges are moving. However, as is shown in this paper, if one assumes that the interaction between moving electric charges is entirely due to the magnetic field, then the same relativistic force transformation equations make it imperative that a second field - this time the electric field - is also present. Therefore, since it is impossible to interpret both the electric and the magnetic field as relativistic effects, one must conclude that neither field is a relativistic effect. The true meaning of the calculations demonstrating the alleged relativistic nature of the magnetic field and of the calculations presented in this paper is, therefore, that the idea of a single force field, be it magnetic or electric, is incompatible with the relativity theory.