Kenya's President William Ruto announced Wednesday the deployment of troops to eastern Democratic Republic of Congo in a joint regional operation against a rebel offensive.
Armed groups in eastern DRC have stepped up attacks, reviving ancient animosities and unleashing a surge in tension with neighbouring Rwanda.
Leaders of the East African Community (EAC) agreed in April to establish a joint force to help restore security in the region.
Speaking at a ceremony in Nairobi, Ruto said the troops were "on a mission to protect humanity".
"As neighbours, the destiny of DRC is intertwined with ours," he added.
"We will not allow any armed groups, criminals and terrorists to deny us our shared prosperity."
Command the force
Kenya will command the force, which will also include soldiers from Burundi, Uganda and South Sudan.
A Rwandan contingent will be deployed along the border, after Kinshasa objected to Kigali's participation in any operations within the DRC.
Military officials in Nairobi declined to reveal the number of Kenyan soldiers involved, citing "obvious security reasons".
A UN force, known by its French acronym of MONUSCO, is already operating in the DRC. Uganda and Burundi also sent troops to the DRC earlier at the invitation of the Congolese government.
The M23 rebels, a mostly Congolese group, resumed fighting in late 2021 after lying dormant for years, accusing the DRC government of failing to honour an agreement to integrate its fighters into the army.
Fresh advances by the militia across North Kivu province last month prompted the UN peacekeeping mission there to increase its alert level and boost support for the Congolese army.
The M23's resurgence has had resounding repercussions for relations in central Africa.
The DRC accuses Rwanda of backing the militia, claims denied by Kigali.
On Saturday, Kinshasa decided to expel Rwanda's ambassador. In turn, Rwanda accused Kinshasa of being "on the path of continued military escalation."
The increase in violence has alarmed the international community, with the African Union appealing for a ceasefire.