Colombian President Gustavo Petro has reignited a long-standing border dispute with Peru, accusing it of “annexing” Santa Rosa Island in the Amazon after Peru declared the territory a district in June—an action Petro says violates existing border treaties.

Santa Rosa Island, which surfaced naturally post-treaty era, faces the Colombian city of Leticia, and its recent elevation to official district status in Peru’s Loreto region has escalated tensions. Colombia contest the action, citing historical treaties that did not account for newly formed river islands.