Abstract The present paper focuses on the antecedents of solidarity behavior towards Ukrainian refugees, specifically examining the role of subjective uncertainty generated in public opinion by the aggression of Ukraine on feelings of compassion and perceptions of refugees as a threat. Based on pooled data from six representative samples collected in different waves during the first six months of the Russian army’s invasion of Ukraine among a representative sample of adult Italian citizens (N = 6,063), the study provided support for the intensification hypothesis, suggesting that uncertainty can act as an affective amplifier. Indeed, the results showed that uncertainty increased perceptions of refugees as a threat (acting on its emotional component, i.e., anxiety), but also feelings of compassion, which is a main driver of solidarity. Moreover, compassion seemed to reduce the (perceived) threat posed by refugees on an economic, cultural, security, or political level. The pattern of relationships tested in the model proved to be stable across different areas of the country and for the first 6 months of the Russian invasion, suggesting that the empathic concern generated by the suffering of the Ukrainian population under attack did not significantly diminish its effects over the period considered.