  (Abridged) Since its launch in October 2002, the INTEGRAL satellite has
revolutionized our knowledge of the hard X-ray sky thanks to its unprecedented
imaging capabilities and source detection positional accuracy above 20 keV.
Nevertheless, many of the newly-detected sources in the INTEGRAL sky surveys
are of unknown nature. The combined use of available information at longer
wavelengths (mainly soft X-rays and radio) and of optical spectroscopy on the
putative counterparts of these new hard X-ray objects allows us to pinpoint
their exact nature. Continuing our long-standing program that has been running
since 2004, and using 6 different telescopes of various sizes, we report the
classification through optical spectroscopy of 22 more unidentified or poorly
studied high-energy sources detected with the IBIS instrument onboard INTEGRAL.
We found that 16 of them are active galactic nuclei (AGNs), while the remaining
6 objects are within our Galaxy. Among the identified extragalactic sources, 14
are Type 1 AGNs; of these, 6 lie at redshift larger than 0.5 and one has z =
3.12, which makes it the second farthest object detected in the INTEGRAL
surveys up to now. The remaining AGNs are of type 2, and one of them is a pair
of interacting Seyfert 2 galaxies. The Galactic objects are identified as two
cataclysmic variables, one high-mass X-ray binary, one symbiotic binary and two
chromospherically active stars. We thus still find that AGNs are the most
abundant population among hard X-ray objects identified through optical
spectroscopy. Moreover, we note that the higher sensitivity of the more recent
INTEGRAL surveys is now enabling the detection of high-redshift AGNs, thus
allowing the exploration of the most distant hard X-ray emitting sources and
possibly of the most extreme blazars.
