Advances being made by the M23 rebel group in the Democratic Republic of Congo are "heightening the threat of a regional war," according to U.N. Secretary General Antonio Guterres.

Congolese troops pushed back an attempted overnight advance by Rwanda-backed rebels on the eastern city of Goma, two Congolese army sources said on Saturday, after the sound of nearby heavy bombardment rocked the city in the early hours.

Fighting has escalated sharply in recent weeks in eastern Congo, where rebels have seized key towns and are closing in on the city of Goma, the government’s last stronghold in the North Kivu province,