Congolese President Felix Tshisekedi and Rwandan President Paul Kagame will attend a summit on Saturday on the crisis in the eastern Democratic Republic of Congo where a Rwanda-backed armed group is advancing.
M23 fighters and Rwandan soldiers have made substantial gains in the eastern DRC, taking the major city of Goma last week, and have vowed to march across the vast country to the capital Kinshasa.
With tensions spiralling, Tshisekedi has promised a "vigorous" military response and urged the international community to impose sanctions on Rwanda.
Tshisekedi and Kagame will join a two-day joint summit of eastern and southern African countries due to begin on Friday in Tanzania, Kenya's presidency said Monday.
Both leaders have been no-shows at previous talks attempting to broker peace between the two sides.
The lightning offensive is the latest escalation in a region devastated by decades of fighting involving dozens of armed groups, with many seeking to control its rich veins of key minerals used in technology.
The fall of Goma, the capital of North Kivu province, saw deadly clashes and added to an already dire humanitarian situation.
The M23 has since advanced towards the neighbouring province of South Kivu, threatening its main city, Bukavu.
A local source in Bukavu told AFP that the city "remains calm for the time being".
But the source added that information suggested that the M23 "is reorganising with reinforcements and arms shipments to probably go to the front now that fighting has ended in Goma".
In South Africa, President Cyril Ramaphosa vowed Monday to continue providing support to the DRC in the face of nationwide calls to withdraw troops following the death of 14 South African soldiers.
"The mission will wind down in accordance with the implementation of various confidence-building measures and when the ceasefire we have called for takes root," Ramaphosa said in a statement.
Most of the soldiers killed were part of a peacekeeping mission sent to the eastern DRC in 2023 by the 16-nation Southern African Development Community (SADC).
- Spat with Rwanda -
Amid an ongoing war of words between Ramaphosa and Kagame, Rwandan government spokeswoman Yolande Makolo reacted strongly to the South African leader's statement.
"You are sending your troops to fight (Congolese President Felix) Tshisekedi's war to kill his own people," she said to Ramaphosa on X.
"Please tell your people the truth about the personal interests in mining that you have in the DRC -- these are the interests for which, sadly, (South African army) SANDF soldiers are dying."
Kagame has said that South African troops have no place in eastern DRC and are a "belligerent force engaging in offensive combat operations to help the DRC government fight against its own people".
A UN expert report said last year that Rwanda had thousands of troops in the DRC seeking to profit from the mining of rare minerals -- and that Kigali has "de facto" control over the M23.
Rwanda has never admitted to military involvement in support of the M23 group and alleges that the DRC supports and shelters the FDLR, an armed group created by ethnic Hutus who massacred Tutsis during the 1994 Rwandan genocide.
South Africa dominates the SADC force, which is estimated to number around 1,300 troops, but Malawi and Tanzania also contribute soldiers.
The United States announced Monday it was further reducing its staff at its embassy in Kinshasa.
By Hillary Orinde