In a fiber structure woven as a single piece by three-dimensional weaving, first weft yarns interlink layers of warp yarns in a first portion of the fiber structure adjacent to a non-interlinked zone and also warp yarns of a second portion of the fiber structure beyond the non-interlinked zone, and second weft yarns interlink layers of warp yarns of the second portion of the fiber structure adjacent to the non-interlinked zone and also layers of warp yarns of the first portion of the fiber structure beyond the non-interlinked zone, such that the paths of the first and second weft yarns cross in at least one transition zone extending within the fiber structure from the end of the non-interlinked zone, the transition zone extending in the weft direction over a distance greater than the pitch between adjacent warp columns.