CH_3_CN towards G10.47+0.03 and G31.41+0.31.

We have used the IRAM 30-m telescope to map, in the J=6-5, J=8-7, and J=12-11 rotational transitions of methyl cyanide (CH_3_CN), the two ultracompact Hii regions G10.47+0.03 and G31.41+0.31. We also detected transitions of vibrationally excited v_8_=1 CH_3_CN and of the isotopomer ^13^CH_3_CN. These observations confirm the existence of hot and dense molecular clumps around the sources, as indicated by Olmi et al.. We extend their work here, through the use of (i) mapping of the two sources, (ii) different techniques to analyse the data, and (iii) detection and description of a velocity shift across the core of G31.41+0.31, whose origin is unclear but it can be interpreted as being due to rotation. Therefore, the observations furnish an independent estimate of temperature and density to compare with those previously obtained from NH_3_ and C^34^S. Temperatures and column densities for the two sources were determined on the basis of the intensities of the optically thin lines, as well as employing the optically thick lines. We conclude that the temperature of the G10.47 and G31.41 cores, on a size scale of 1.5", is about 160K and 140K, respectively. We indirectly estimate the hot-cores angular size (<2"), and can also infer the existence of an extended envelope (>=10"). The molecular abundance ratio [CH_3_CN]/[NH_3_] is of order of 0.01 in both sources. We also infer a mass of roughly 10^3^M_sun_ inside a region of order 0.1pc in the case of G31.41+0.31, and a rather similar situation is found for G10.47+0.03. From this information, it seems reasonable to speculate that we may be observing an early phase of the evolution of a galactic cluster.