  We study the hard X-ray (20-100 keV) variability of the Galactic Center (GC)
and of the nearby sources on the time scale of 1000 s. We find that 3 of the 6
hard X-ray sources detected by INTEGRAL within the central 1 degree of the
Galaxy are not variable on this time scale: the GC itself (the source IGR
J1745.6-2901) as well as the source 1E 1743.1-2843 and the molecular cloud Sgr
B2. We put an upper limit of 5 x 10^{-12} erg/(cm^2 sec) (in 20 to 60 keV band)
on the variable emission form the supermassive black hole (the source Sgr A*)
which powers the activity of the GC(although we can not exclude the possibility
of rare stronger flares). The non-variable 20-100 keV emission from the GC
turns out to be the high-energy non-thermal tail of the diffuse hard ``8 keV''
component of emission from Sgr A region. Combining the XMM-Newton and INTEGRAL
data we find that the size of the extended hard X-ray emission region is about
20 pc. The only physical mechanism of production of diffuse non-thermal hard
X-ray flux, which does not contradict the multi-wavelength data on the GC, is
the synchrotron emission from electrons of energies 10-100 TeV.
