  We report a study of the stellar content of the Near-infrared cluster
[DBS2003]\,157 embedded in the extended H\,{\sc ii} region GAL\,331.31-00.34,
which is associated with the IRAS source 16085-5138. $JHK$ photometry was
carried out in order to identify potential ionizing candidates, and the
follow-up NIR spectroscopy allowed the spectral classification of some sources,
including two O-type stars. A combination of NIR photometry and spectroscopy
data was used to obtain the distance of these two stars, with the method of
spectroscopic parallax: IRS\,298 (O6\,{\sc V}, $3.35 \pm 0.61$\,kpc) and
IRS\,339 (O9\,{\sc V}, $3.24 \pm 0.56$\,kpc). Adopting the average distance of
$3.29 \pm 0.58$\,kpc and comparing the Lyman continuum luminosity of these
stars with that required to account for the radio continuum flux of the H\,{\sc
ii} region, we conclude that these two stars are the ionizing sources of
GAL\,331.31-00.34. Young stellar objects (YSOs) were searched by using our NIR
photometry and MIR data from the GLIMPSE survey. The analysis of NIR and MIR
colour-colour diagrams resulted in 47 YSO candidates.
  The GLIMPSE counterpart of IRAS\,16085-5138, which presents IRAS colour
indices compatible with an ultra-compact H\,{\sc ii} region, has been
identified. The analysis of its spectral energy distribution between 2 and
$100\,\mu$m revealed that this source shows a spectral index $\alpha = 3.6$
between 2 and $25\,\mu$m, which is typical of a YSO immersed in a protostellar
envelope. Lower limits to the bolometric luminosity and the mass of the
embedded protostar have been estimated as $L=7.7\times10^3L_{\sun}$ and $M =
10\,M_{\sun}$, respectively, which corresponds to a B0--B1\,{\sc V} ZAMS star.
