A search for scalar and vector leptoquarks coupling to first generation fermions is performed in the H1 experiment at the ep collider HERA. The analysis uses e-p data collected in 1998 and 1999 at a centre-of-mass energy of 320 GeV, corresponding to an integrated luminosity of similar to 15 pb(-1). No evidence for the direct production of such particles is found in a data sample with a large transverse momentum final state electron or with large missing transverse momentum, and constraints on leptoquark models are established. For a Yukawa coupling of electromagnetic strength leptoquarks are excluded for masses up to similar to 290 GeV. This analysis complements the leptoquark searches performed previously using data collected whilst HERA was operating with positrons instead of electrons. (C) 2001 Elsevier Science B.V. All rights reserved.