brightest region at optical and radio wavelengths [e.g., @felli90]. Both extended radio sources were detected at several frequencies [e.g., @shaver70; @haynes78]. Detailed studies of these two bright regions were performed using VLA observations at 5 GHz with an angular resolution of 100 [@felli90]. Optical images of the whole NGC 6357 region show a number of additional ionized regions, with no previous optical and radio studies.

The distribution of the molecular gas associated with selected regions in the complex was investigated by @mcbreen83 and @massi97. These last authors found that the bulk of the molecular gas related to the complex has velocities in the range \[-14,+4\] .

The massive open cluster Pis24, which lies in the central cavity of NGC6357 and has an age of about 210$^6$ yr, is considered to be the only ionization source of the complex because of the huge number of UV photons emitted by the massive stars [@massey01]. The cluster contains at least a dozen O-type stars [@wang07], including two of the most luminous stars known in the Galaxy [@bohigas04]. These stars were classified O3.5If (Pis24-1) and O3.5III(f\*) (Pis24-17) by @walborn02. Recent studies by @maizapellaniz07 showed that Pis24-1 is a multiple system. The Wolf-Rayet star WR93 