We present new millimeter and infrared spectroscopic observations towards the radio nebula G10.0 - 0.3 , which is powered by the wind of the Luminous Blue Variable star LBV 1806 - 20 also closely associated with the soft gamma-ray repeater SGR 1806 - 20 , and believed to be located in the giant Galactic H ii complex W31 .
Based on observations of CO emission lines and NH _ { 3 } absorption features from molecular clouds along the line of sight to G10.0 - 0.3 , as well as the radial velocity and optical extinction of the star powering the nebula , we determine its distance to be 15.1 ^ { +1.8 } _ { -1.3 } kpc in agreement with Corbel et al .
( 1997 ) .
In addition , this strengthens the association of SGR 1806 - 20 with a massive molecular cloud at the same distance .
All soft gamma-ray repeaters with precise location are now found to be associated with a site of massive star formation or molecular cloud .
We also show that W31 consists of at least two distinct components along the line of sight .
We suggest that G10.2 - 0.3 and G10.6 - 0.4 are located on the - 30 km s ^ { -1 } spiral arm at a distance from the Sun of 4.5 \pm 0.6 kpc and that G10.3 - 0.1 may be associated with a massive molecular cloud at the same distance as the LBV star , i.e .
15.1 ^ { +1.8 } _ { -1.3 } kpc , implying that W31 could be decomposed into two components along the line of sight .