  We report the first observation of an anisotropy in the arrival direction of
cosmic rays with energies in the multi TeV region in the Southern sky using
data from the IceCube detector. Between June 2007 and March 2008, the
partially-deployed IceCube detector was operated in a configuration with 1320
digital optical sensors distributed over 22 strings at depths between 1450 and
2450 meters inside the Antarctic ice. IceCube is a neutrino detector, but the
data are dominated by a large background of cosmic ray muons. Therefore, the
background data are suitable for high-statistics studies of cosmic rays in the
Southern sky. The data include 4.3 billion muons produced by downgoing cosmic
ray interactions in the atmosphere; these events were reconstructed with a
median angular resolution of 3 degrees and a median energy of $\sim20$ TeV.
Their arrival direction distribution exhibits an anisotropy in right ascension
with a first harmonic amplitude of $(6.4\pm0.2 $stat$. \pm 0.8
$syst$.)\times10^{-4}$.
