Rwanda-backed rebels claimed they captured eastern Congo’s strategic city of Goma, the hub of a region containing trillions of dollars in mineral wealth that remains largely untapped, the Associated Press reported.

The Government of the Democratic Republic of Congo (DRC) said Monday that the “Rwandan Army” is in the strategic Congolese city of Goma (northeast), taken by the rebel group Mar. 23 Movement (M23), allegedly supported by neighboring Rwanda.

Rwandan President Paul Kagame has lashed out at South African counterpart Cyril Ramaphosa, after Ramaphosa accused Rwanda of backing the M23 rebels behind the escalating crisis in the eastern Democratic Republic of Congo this week.

Democratic Republic of Congo President Felix Tshisekedi has vowed “a vigorous and coordinated response” against a rebel alliance that has besieged swaths of the nation’s mineral-rich east and forced hundreds of local troops and foreign mercenaries to surrender.

M23 rebels in the Democratic Republic of Congo were reported to have taken the key eastern city of Goma in fierce fighting with government forces that sent streams of refugees fleeing area communities.

Congolese security forces on Tuesday tried to slow the advance of Rwanda-backed M23 rebels who say they have captured Goma after entering eastern Congo’s largest city, as U.N. officials reported violence,

The United Nations expressed deep concern at reports of M23 rebels and Rwandan troops advancing south towards the Congolese city of Bukavu on Thursday, as the militants sought also to assert their control over east Congo's largest city Goma.

M23 rebels, with support from Rwandan troops, marched into Goma earlier this week and are now advancing south toward Bukavu.

Nearly 300 foreign mercenaries hired by the Democratic Republic of Congo government to counter a swift offensive by Rwandan-backed M23 rebels in the east have surrendered and were on their way home on Wednesday.

The Rwanda-backed armed group M23 vowed on Thursday to march on the DR Congo capital, Kinshasa, as its fighters made further advances in the mineral-rich east of the country.

By Yassin Kombi and Sonia Rolley GOMA, Democratic Republic of Congo (Reuters) -President Paul Kagame said Rwanda was ready for "confrontation" as he rejected criticism over his backing for M23 rebels who were pushing south on Thursday in eastern Democratic Republic of Congo after capturing the major city of Goma.