  Aims: Recurrent nova systems like RS Oph have been proposed as a possible
channel to Type Ia Supernova explosions, based on the high mass of the
accreting white dwarf. Additional support to this hypothesis has been recently
provided by the detection of circumstellar material around SN2006X and
SN2007le, showing a structure compatible with that expected for recurrent nova
outbursts.In this paper we investigate the circumstellar environment of RS Oph
and its structure, with the aim of establishing a firmer and independent link
between this class of objects and Type Ia SN progenitors.
  Methods: We study the time evolution of CaII, NaI and KI absorption features
in RS Oph, before, during, and after the last outburst, using multi-epoch,
high-resolution spectroscopy, and applying the same method adopted for SN2006X
and SN2007le.
  Results: A number of components, blue-shifted with respect to the systemic
velocity of RS Oph, are detected. In particular, one feature strongly weakens
in the first two weeks after the outburst, simultaneously with the
disappearance of very narrow P-Cyg profiles overimposed on the much wider nova
emission lines of H, He, FeII and other elements.
  Conclusions: We interpret these facts as the signature of density
enhancements in the circumstellar material, suggesting that the recurrent
eruptions might indeed create complex structures within the material lost by
the donor star. This establishes a strong link between RS Oph and the
progenitor system of the Type Ia SN2006X, for which similar features have been
detected.
