  Observations of two unclassified Low Mass X-ray Binaries, X1543-624 and
X1556-605, are presented. In the 2-10 keV band the first of the two sources is
a factor two stronger than the other. Both sources do not show X-ray bursts,
dips or eclipses in their X-ray light curves. We find that both spectra are
described by a two-component model consisting of emission from a cool accretion
disk plus a Comptonized blackbody with kTbb ~ 1.5 keV in a low opacity plasma.
The spectrum of X1543-624 hardens from the first to the second observation,
when the source slowly moves from right to left in the colour-colour diagram.
The spectrum of X1556-605 can also be described by a model consisting of a
blackbody plus an unsaturated Comptonization with electron energy kTe ~ 4 keV.
In the first observation, X1543-624 shows evidence of a Fe K emission line at
6.4 keV. Moreover in both observations, the source spectrum exhibits an
emission feature around 0.7 keV, which is interpreted as due to the
superposition of the K edge absorption features of O and Ne elements with
uncommon relative abundances with respect to the solar one (O/O(sun) ~0.3,
Ne/Ne(sun) ~ 2.5). In the spectrum of X1556-605 no emission lines are observed.
We discuss these results and their implications on the source classification
and the accretion geometry on the compact object.
