KHARTOUM, July 12 -- The Sudanese army announced Wednesday it had retaken the border town of Kurmuk from the Rapid Support Forces after more than three months of occupation, a gain that arrived alongside deepening alarm over El-Obeid, a city of half a million, where RSF drone strikes have killed at least 50 civilians in ten consecutive days and aid workers warn of an imminent atrocity.

The two developments define the contradictory logic the war has settled into in its fourth year. The army reclaims territory at one end of the country while the RSF tightens a siege at the other.

Kurmuk, which sits on Sudan's border with Ethiopia in Blue Nile state, fell to the RSF and an allied faction of the Sudan People's Liberation Movement on March 2...