  Within the framework of our program of assessment of the nature of
unidentified or poorly known INTEGRAL sources, we present here spectroscopy of
optical objects, selected through positional cross-correlation with soft X-ray
detections (afforded with satellites such as Swift, ROSAT, Chandra and/or
XMM-Newton) as putative counterparts of hard X-ray sources detected with the
IBIS instrument onboard INTEGRAL. Using 6 telescopes of various sizes and
archival data from two on-line spectroscopic surveys we are able to identify,
either for the first time or independent of other groups, the nature of 20
INTEGRAL hard X-ray sources. Our results indicate that: 11 of these objects are
active galactic nuclei (AGNs) at redshifts between 0.014 and 0.978, 7 of which
display broad emission lines, 2 show narrow emission lines only, and 2 have
unremarkable or no emission lines (thus are likely Compton thick AGNs); 5 are
cataclysmic variables (CVs), 4 of which are (possibly magnetic) dwarf novae and
one is a symbiotic star; and 4 are Galactic X-ray binaries (3 with high-mass
companions and one with a low-mass secondary). It is thus again found that the
majority of these sources are AGNs or magnetic CVs, confirming our previous
findings. When possible, the main physical parameters for these hard X-ray
sources are also computed using the multiwavelength information available in
the literature. These identifications support the importance of INTEGRAL in the
study of the hard X-ray spectrum of all classes of X-ray emitting objects, and
the effectiveness of a strategy of multi-catalogue cross-correlation plus
optical spectroscopy to securely pinpoint the actual nature of unidentified
hard X-ray sources.
