Let M be an n-dimensional complete immersed submanifold with parallel mean curvature vectors in an (n+p)-dimensional Riemannian manifold N of constant curvature c > 0. Denote the square of length and the length of the trace of the second fundamental tensor of M by S and H, respectively. We prove that if
S ≤ 1/(n-1) H² + 2c, n ≥ 4,
S ≤ 1/2 H² + min(2,(3p-3)/(2p-3))c, n = 3,
then M is umbilical. This result generalizes the Okumura-Hasanis pinching theorem to the case of higher codimensions.