"It is a positive development and it is clearly better than nothing. For the last two weeks we have been asking for a window to bring in ambulances to take away at least 200 wounded, some of them children," de Mistura told Svenska Dagbladet newspaper in an interview.
"We have seen in the past that were promising statements, which were later washed out or complicated by conditions. There is a serious risk that this could happen now. But this is better than nothing," de Mistura stressed.
Earlier in the day, the Russian Defense Ministry extended for three more hours the previously announced humanitarian pause in Aleppo, which would start from 08:00 local time (05:00 GMT) on October 20 and run through 19:00 local time.
Aleppo has been engulfed in a heavy fighting since the government forces began a major offensive on the rebel-held eastern districts of the city following the collapse of the ceasefire brokered by Russia and the United States in early September.