Despite many years of observations, the mechanism behind gamma-ray bursts (GRBs) prompt emission (~100keV-1MeV) is still largely uncertain. Several models have been proposed; among them synchrotron, the most largely admitted but showing some difficulties. Inverse Compton mechanisms seemed promising; however, synchro self-Compton (SSC) was shown to lead to an energy crisis, and the lack of strong GeV component in observations rules it out. We explore the possibility of external inverse-Compton (EIC), where seed photons comes from an object external to the GRB itself; this releases most energy constraints of SSC. We describe three promising candidate configurations, but show that strong constraints apply to them and that they are most probably ruled out.