  The sharp suppression of the de-Haas van-Alphen oscillations observed in the
mixed superconducting (SC) state of the heavy fermion compound URu$_{2}$Si$%
_{2}$ is shown to confirm a theoretical prediction of a narrow double-stage SC
phase transition, smeared by fluctuations, in a 3D paramagnetically-limitted
superconductor. The predicted scenario of a second order transition to a
nonuniform (FFLO) state followed by a first order transition to a uniform SC
state, obtained by using a non-perturbative approach, is also found to be
consistent with recent thermal conductivity measurements performed on this
material.
