  We have derived a new system of mKdV-type equations which can be related to
the affine Lie algebra $A_{5}^{(2)}$. This system of partial differential
equations is integrable via the inverse scattering method. It admits a
Hamiltonian formulation and the corresponding Hamiltonian is also given. The
Riemann-Hilbert problem for the Lax operator is formulated and its spectral
properties are discussed.
