  We show that pQCD factorization incorporated with pre-haronization
energy-loss effect naturally leads to flatness of the nuclear modification
factor R_{AA} for produced hadrons at high transverse momentum p_T. We consider
two possible scenarios for the pre-hadronization: In scenario 1, the produced
gluon propagates through dense QCD medium and loses energy. In scenario 2, all
gluons first decay to quark-antiquark pairs and then each pair loses energy as
propagating through the medium. We show that the estimates of the energy-loss
in these two different models lead to very close values and is able to explain
the suppression of high-p_T hadrons in nucleus-nucleus collisions at RHIC. We
show that the onset of the flatness of R_{AA} for the produced hadron in
central collisions at midrapidity is about p_T\approx 15 and 25 GeV at RHIC and
the LHC energies, respectively. We show that the smallness (R_{AA}<0.5) and the
high-p_T flatness of R_{AA} obtained from the k_T factorization supplemented
with the Balitsky-Kovchegov (BK) equation is rather generic and it does not
strongly depend on the details of the BK solutions. We show that energy-loss
effect reduces the nuclear modification factor obtained from the k_T
factorization about 30\div 50% at moderate p_T.
