Homogeneous Riemannian manifolds of positive Ricci curvature

We prove that a homogeneous effective space M = G/H, where G is a connected Lie group and H subset of G is a compact subgroup, admits a G-invariant Riemannian metric of positive Ricci curvature if and only if the space M is compact and its fundamental group pi(1)(M) is finite (in this case any normal metric on G/H is suitable). This is equivalent to the following conditions: the group G is compact and the largest semisimple subgroup LG subset of G is transitive on G/H. Furthermore, if G is nonsemisimple, then there exists a G-invariant fibration of M over an effective homogeneous space of a compact semisimple Lie group with the torus as the fiber.