Burundi is withdrawing its forces from eastern Democratic Republic of Congo where they had been fighting against M23 rebels, four sources said on Tuesday, in a further blow to Congo's army as it struggles to halt a rebel advance.

Residents say Rwanda-backed rebels appear to be heading toward a third major city in eastern Congo. International pressure rose Tuesday over the M23’s expansion in the mineral-rich region that’s critical for global technology.

M23 rebels backed by Rwanda took the city of Goma in a bloody battle. This weekend, the group entered the gold-trading center of Bukavu in eastern Congo after government soldiers fled.