Isometric spacelike immersions of space forms in indefinite space forms

Let M be a connected n-dimensional space form spacelike isometrically immersed in a (2n −1) dimensional indefinite space form. If M is maximal, we prove that either M is totally geodesic or M is a piece of the n-dimensional hyperbolic cylinder in the (2n −1)-dimensionaal pseudo-hyperbolic space.