Constant strain rate molecular dynamics simulations under the modified boundary conditions were performed to elucidate the interaction processes between the kink motion of screw dislocation and the glissile self-interstitial atom cluster loops in bcc Fe by using an EAM potential for Fe fitted to ab initio forces. The junction formation and the helical dislocation mechanisms were identified as two possible interaction processes. In the junction mechanism, the initial Burgers vector 1/2<111> of the cluster loop was transformed into <100>. In the helical dislocation mechanism first the absorption, followed by the formation of the helical dislocation and the emission of the cluster loop through Hirsch mechanism was observed. Substantial hardening was seen as result of the interactions. The stress-strain plots obtained for different loop sizes, temperature and strain rates were used to estimate the strengthening factors.