  We present results for the renormalization constants of bilinear quark
operators obtained by using the tree-level Symanzik improved gauge action and
the Nf=2 twisted mass fermion action at maximal twist, which guarantees
automatic O(a)-improvement. Our results are also relevant for the corresponding
standard (un-twisted) Wilson fermionic action since the two actions only
differ, in the massless limit, by a chiral rotation of the quark fields. The
scale-independent renormalization constants ZV, ZA and the ratio ZP/ZS have
been computed using the RI-MOM approach, as well as other alternative methods.
For ZA and ZP/ZS, the latter are based on both standard twisted mass and
Osterwalder-Seiler fermions, while for ZV a Ward Identity has been used. The
quark field renormalization constant Zq and the scale dependent renormalization
constants ZS, ZP and ZT are determined in the RI-MOM scheme. Leading
discretization effects of O(g^2 a^2), evaluated in one-loop perturbation
theory, are explicitly subtracted from the RI-MOM estimates.
