William Ruto sends troops to the Democratic Republic of the Congo to halt the rebel advance.
Kenyan President William Ruto announced the deployment of troops to the eastern Democratic Republic of the Congo in a joint regional operation to counter a rebel offensive on Wednesday.
Armed groups have increased their attacks in eastern DRC, reigniting old animosities and escalating tensions with neighboring Rwanda.
East African Community (EAC) leaders agreed in April to form a joint force to help restore regional security.
Ruto stated at a ceremony in Nairobi that the troops were "on a mission to protect humanity."
"As neighbors, DRC's fate is intertwined with ours," he added.
"We will not let armed groups, criminals, or terrorists deny us our common prosperity."
The force, which will include soldiers from Burundi, Uganda, and South Sudan, will be led by Kenya.
After Kinshasa objected to Kigali's participation in any operations within the DRC, a Rwandan contingent will be deployed along the border.
Nairobi military officials refused to reveal the number of Kenyan soldiers involved, citing "obvious security reasons."
In the DRC, a UN force known by its French acronym MONUSCO is already in place. Earlier, Uganda and Burundi sent troops to the DRC at the invitation of the Congolese government.
After lying dormant for years, the M23 rebels, mostly Congolese, resumed fighting in late 2021, accusing the DRC government of failing to honor an agreement to integrate its fighters into the army.
Last month, new militia advances in North Kivu province prompted the UN peacekeeping mission to raise its alert level and increase support for the Congolese army.
The M23's resurgence has had far-reaching consequences for Central African relations.
The DRC accuses Rwanda of assisting the militia, which Kigali denies.
Kinshasa decided to recall Rwanda's ambassador on Saturday. Rwanda, for its part, accused Kinshasa of being "on the verge of further military escalation."
The uptick in violence has alarmed the international community, prompting the African Union to call for a cease-fire.