In this paper, we establish an achievable rate region for discrete memoryless interference relay channel (DM-IRC) that consists of two source-destination pairs and a single relay by applying a combination of Han-Kobayashi and noisy network coding schemes. Using this strategy, we characterize the capacity region of a class of DM-IRCs. This class of DM-IRCs naturally generalizes the injective deterministic discrete memoryless interference channel by El Gamal and Costa and the deterministic discrete memoryless relay channel with orthogonal receiver components by Kim. For converse, a genie-aided proof technique is used. Furthermore, we achieve the symmetric capacity of Gaussian interference relay channel with orthogonal receiver components to within a constant number of bits by using Han-Kobayashi and noisy network coding schemes.