  A system of field equations for an Einstein-Maxwell model with $RF^2$-type
nonminimal coupling in a non-Riemannian space-time with a non-vanishing torsion
is derived and the resulting field equations are expressed in terms of the
Riemannian quantities based on a metric with a Lorentzian signature. The
torsion is generated by the gradients of the electromagnetic field invariants.
An electromagnetic constitutive tensor is introduced in the formulation of the
field equations.
