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 United States urged the United Nations Security Council on Tuesday to consider measures to halt an offensive by Rwandan troops and M23 rebel forces in eastern Democratic Republic of Congo as a conflict there escalates.

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.