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

Three U.N. peacekeepers from South Africa have been killed in fighting M23 rebels in eastern Congo, a political party and a trade union said Saturday. The peacekeepers were killed on Thursday. M23 has made significant territorial gains in recent weeks,

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,