U.S. Secretary of State Marco Rubio told Rwandan President Paul Kagame on Tuesday that Washington was "deeply troubled" by escalation in the conflict in the Democratic Republic of Congo, particularly the fall of the city of Goma to Rwandan-backed rebels.

A conflict that has raged for decades reached a flashpoint this week when rebels backed by Rwanda marched on a key Congolese city in a bid to occupy territory and exploit minerals.

The volatile situation in the Democratic Republic of Congo has a long history. Here's what you need to know.Surging violence in the Democratic Republic of Congo, has ignited fears of large-scale instability in one of Africa's most conflict-ridden countries.

M23 rebels captured the key city of Goma in the eastern DRC Monday, forcing thousands of civilians to flee in the latest in a series of advances - Anadolu Ajansı

Rwanda-backed M23 rebels faced pockets of resistance from army and pro-government militia overnight after entering eastern Congo's largest city Goma in the worst escalation of a conflict that has run for more than a decade.

Fighting between Rwanda-backed rebels and the Congolese army continued for a second day in Goma on Tuesday amid calls by African leaders for an immediate ceasefire.

United Nations Secretary-General Antonio Guterres held talks with the presidents of the Democratic Republic of Congo and Rwanda to address the escalating conflict in eastern Congo. Emphasis was placed on civilian safety amid allegations of Rwandan support for M23 rebels in the region.

United Nations Secretary-General Antonio Guterres on Tuesday spoke separately with the presidents of the Democratic Republic of Congo and Rwanda about the escalating conflict in eastern Congo, U.N. spokesperson Stephane Dujarric said.

Four more South African soldiers were killed in the eastern Democratic Republic of the Congo, bringing the total number of peacekeepers killed to 17 as clashes with M23 rebels continued, media reports said on Tuesday.