[en] Neutral test particles around a Schwarzschild black hole immersed in an external uniform magnetic field have no interactions of electromagnetic forces, but their motions can be chaotic. This chaotic behaviour is induced by the gravitational effect of the magnetic field, leading to the nonintegrability of the magnetized Ernst-Schwarzschild spacetime geometry. Chaos is strengthened typically as the energy or the magnetic field increases under appropriate circumstances. When these particles have charges, electromagnetic forces are included. As a result, electromagnetic forces strengthen or weaken the extent of chaos caused by the gravitational effect of magnetic field.