  GRB 970828 was the first well-localized gamma-ray burst (GRB) X-ray afterglow
for which no optical afterglow was found despite a prompt, deep search down to
R_lim ~ 24.5 mag. We report the discovery of a short-lived radio flare within
the X-ray localization error circle of this burst. Such radio flares are seen
in about 25% of GRB afterglows and their origin is not well understood. The
precise radio position enabled us to identify the likely host galaxy of this
burst, and to measure its redshift, z = 0.9578. The host appears to be an
interacting/merging system. Under the assumption that the X-ray afterglow is
mainly due to synchrotron mechanism we infer the optical afterglow flux. The
observed upper limits to the optical flux are easily explained by invoking an
intervening dusty cloud within the host galaxy. These observations support the
idea that GRBs with no detectable optical afterglows or "dark GRBs" can be due
to dust extinction within the host galaxies. The census of dark GRBs can then
be used to constrain the fraction of the obscured star formation in the
universe. We argue that the existing data already indicate that the obscured
star-formation rate is no more than 1/2 of that seen at UV and optical
wavelengths.
