Rwanda-backed rebels appeared to be heading toward a third major city in eastern Congo, frightened residents said Tuesday, as international pressure rose over the M23's expansion in the mineral-rich region that's critical for global technology.

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.

Burundian troops began withdrawing from eastern Congo, intensifying challenges for the Congolese army facing the advancing M23 rebels. Meanwhile, the U.N. has accused M23 of executing children as conflict-driven chaos impacts civilians,