Rwanda-backed rebels were expanding their presence in eastern Congo after capturing Goma, the region's major city, the U.N. said Friday, also expressing concerns over executions it learned were carried out by the rebels in recent days following a major escalation of their yearslong rebellion.

The Rwandan-backed armed group M23 moved south as it closed in on a key military airport in DR Congo on Friday, a day after pledging to take the capital Kinshasa and as international criticism mounted.