GOMA, Congo — Rebels widely believed to be backed by Rwanda and Uganda held their positions in this key eastern Congolese city that they seized last week, letting a midnight deadline for their withdrawal expire in the early hours of Tuesday.

Trucks loaded with fighters belonging to the eight-month-old M23 rebel group patrolled the empty streets of this regional capital, as the ultimatum issued by the regional bloc representing nations in the Great Lakes region of Central Africa came to an end.