We report the results of extensive high-energy observations of the X-ray transient and black hole candidate XTE J1720-318 performed with INTEGRAL , XMM-Newton and RXTE .
The source , which underwent an X-ray outburst in 2003 January , was observed in February in a spectral state dominated by a soft component with a weak high-energy tail .
The XMM-Newton data provided a high column density N _ { \mathrm { H } } of 1.2 \times 10 ^ { 22 } cm ^ { -2 } which suggests that the source lies at the Galactic Centre distance .
The simultaneous RXTE and INTEGRAL Target of Opportunity observations allowed us to measure the weak and steep tail , typical of a black-hole binary in the so-called High/Soft State .
We then followed the evolution of the source outburst over several months using the INTEGRAL Galactic Centre survey observations .
The source became active again at the end of March : it showed a clear transition towards a much harder state , and then decayed to a quiescent state after April .
In the hard state , the source was detected up to 200 keV with a power law index of \sim 1.9 and a peak luminosity of \sim 7 \times 10 ^ { 36 } erg s ^ { -1 } in the 20-200 keV band , for an assumed distance of 8 kpc .
We conclude that XTE J1720-318 is indeed a new member of the black hole X-ray novae class which populate our galactic bulge and we discuss its properties in the frame of the spectral models used for transient black hole binaries .