  The sigma model describing closed strings rotating in AdS_3 x S^3 is known to
reduce to the one-dimensional Neumann-Rosochatius integrable system. In this
article we show that closed spinning strings in AdS_3 x S^3 x T^4 in the
presence of NS-NS three-form flux can be described by an extension of the
Neumann-Rosochatius system. We consider closed strings rotating with one spin
in AdS_3 and two different angular momenta in S^3. For a class of solutions
with constant radii we find the dependence of the classical energy on the spin
and the angular momenta as an expansion in the square of the 't Hooft coupling
of the theory.
