DAKAR, Senegal — The Democratic Republic of Congo and Rwanda-backed rebels have signed a declaration of principles for a permanent ceasefire in eastern Congo, where ethnic tensions and a quest for rich minerals have resulted in one of Africa’s longest conflicts, with thousands killed this year alone.

Congo and the M23 rebel group on Saturday pledged to sign a peace agreement by Aug. 18, a sign of progress even as outstanding details need to be negotiated. Representatives for both sides were at a ceremony in Doha following months of Qatari mediation.

Congo and Rwanda-backed rebels have signed a declaration in Qatar to end decades of conflict in eastern Congo.