The processes associated with transformations of oxygen-related radiation-induced defects in Czochralski-grown silicon crystals irradiated with fast electrons or neutrons and subjected to heat-treatments in the temperature range 450 – 700 °C have been studied by means of IR absorption spectroscopy. It is found that upon disappearance of the VO3 and VO4 defects the new vacancy-oxygen-related complexes, which give rise to a number of vibrational absorption bands in the 980 – 1115 cm–1 vawenumber range, are formed. It is argued that these complexes are VOm (m ≥ 5) defects which serve as radiation-induced nucleation centers of enhanced oxygen precipitation.