We develop the approach to the problem of neutrino oscillations in a magnetic field introduced
in [1] and extend it to the case of three neutrino generations. The theoretical framework suitable
for computation of the Dirac neutrino spin, flavour and spin-flavour oscillations probabilities in
a magnetic field is given. The closed analytic expressions for the probabilities of oscillations
are obtained accounting for the normal and inverted hierarchies and the possible effect of CP
violation. In general, the neutrino oscillation probabilities exhibit quite a complicated
interplay of oscillations on the magnetic $\omega_B=\mu_{\nu} B$ and vacuum $\omega_{vac}=\frac{\Delta m^2_{ik}}{4p}$
frequencies. The obtained
results are of interest in applications to neutrino oscillations under the influence of extreme
astrophysical environments, for example peculiar to magnetars and supernovas, as well as in
studying neutrino propagation in interstellar magnetic fields (see [2]).