A method and network node of a first cellular network, for enabling mitigation of interference in the first cellular network caused by radio communication in a second cellular network. The network node obtains a total interference in a first cell of the first cellular network, and estimates a first interference contribution in the first cell caused by radio communication in the first cellular network. The network node then determines a second interference contribution in the first cell caused by radio communication in the second cellular network based on the estimated first interference contribution and the obtained total interference. The network node also utilizes the determined second interference contribution to counteract the interference in the first cell caused by the radio communication in the second cellular network. Thereby, it is possible to counteract the interference in the first cell when the second interference contribution fulfills a threshold condition such that actions and measures for counteracting the inter-system interference can be initiated only when needed or when it is deemed effective for improving performance in the cell.