The recently discovered Kuiper belt objects (KBOs) with orbital distances beyond the orbit of Neptune might represent the source population of the short-period comets. From the point of view of evolutionary history, the KBOs must have experienced a period of intensive collisional interactions during and after their accretion. It remains a possibility that, instead of being of pristine nature, a significant fraction of the short-period comets of km-size might be secondary products from collisional fragmentation of the large parent bodies. The physico-chemical properties of some of the cometary nuclei could hence carry important information on the process of thermal differentiation in the interiors of some KBOs with diameters of about a few hundred km.