The strong binding between a vacancy and carbon in bcc iron plays an important role in the evolution of radiation-induced microstructure. Our previous ab initio study points to the fact that the vacancy-carbon (V-C) pair can serve as a nucleus for the solute-rich clusters. Here, we continue the ab initio study by considering the interaction of mixed solute clusters (Mn, Ni and Si) with the V-C pair, and the interaction of typical alloying elements of Fe-based steels (i.e., Mn, Ni, Cu, Si, Cr and P) with di-carbon-vacancy pair (V-C-2). We have identified the sequence of growth of Ni, Si and Mn solute-rich clusters nucleating on the V-C pair. The mixed-solute-V-C configurations are found to be less stable clusters than pure-solute-V-C clusters with the energy difference up to 0.22 eV per four atoms. The V-C-2 pair is found to be as strong nucleation site for the solute-rich clusters as the V-C pair. Only Si solute atom stands out from the trend showing a weaker affinity to the V-C-2 complex by 0.09 eV compared to the attraction to the V-C pair. The overall results point to the importance of taking into account the existence of both V-C and V-C-2 complexes in studying the formation of solute-rich clusters in Fe-based steels for nuclear applications. (C) 2014 Elsevier B.V. All rights reserved.