We study the Euler equations with gravitational source terms derived from a potential which satisfies Poisson's equation for gravity. An adequate treatment of the source terms is achieved by introducing their discretization into an approximate Riemann solver, relying on a relaxation strategy. The associated numerical scheme is then presented and its performance demonstrated. The new method provides a straightforward extension to multidimensions and is applied to different types of problems under gravitational influence, including a one dimensional hydrostatic atmosphere and a three-dimensional Rayleigh-Taylor instability. We show the first results for the implicit version of the scheme, essential for many applications of physical interest and implemented in the code HERACLES.