If gamma-ray bursts originate in our Galaxy, they probably involve violent disturbances in the magnetospheres of neutron stars. Any event of this kind is likely to trigger the sudden expulsion of magnetic flux and plasma at relativistic speed. We show that such ejecta would be braked by the interstellar medium (ISM), and that a gamma-ray flash with duration ~ 0.1 – 100 s may result from this interaction. We suggest that the stronger, ‘smooth’ class of bursts, recently identified from analyses of BATSE data, could result from the deceleration of such a blast wave by the ISM. The radiative efficiency, and hence the detectability, of such bursts would depend on the density of the circumstellar ISM. Therefore, even if the neutron star ‘triggers’ were uniformly distributed in space (at least within 1–2 kpc of the Sun), the observed locations of bursts would correlate with regions of above-average ISM density.