Fighting with M23 rebels in eastern Democratic Republic of Congo left six United Nations peacekeepers dead, UN officials said Saturday.

Congo severed diplomatic ties with Rwanda as fighting between Rwanda-backed rebels and government forces raged around the key eastern city of Goma, leaving at least 13 peacekeepers and foreign soldiers dead and displacing thousands of civilians.

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,