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 Democratic Republic of Congo’s electoral body has accused the Rwandan army and M23 rebels of looting polling office facilities in Goma, a city in eastern Congo.

As Rwanda-backed M23 rebels in eastern Democratic Republic of Congo push south towards the city of Bukavu, they are likely to have to fight their way through thousands of troops from Burundi, ramping up the risk of a return to full-blown regional war.