Maimonides does not say 'show no mercy'; in fact, he makes various provisions for showing mercy. The passage from Jeremiah (48:10) does not say 'show no mercy'. The question I have is: what does the IDF Chief Rabbi mean when he says it is forbidden to show mercy 'when no mercy should be shown'? In what specific circumstances is it possible and yet impermissible to show mercy? And why should the Chief Rabbi not also acknowledge that Maimonides does make provision for giving quarter? We are getting this second hand, but the quotes here do sound like the lazy generalisations of a politician rather than the precision of an authority on religious Jewish texts.
Austrian police say they expect 10,000 migrants to arrive from Hungary (DPA)
from the article: IDF Chief Rabbi: Troops who show mercy to enemy will be 'damned'