Kenya's President William Ruto on Wednesday officially deployed troops to eastern Democratic Republic of Congo to join an East African regional force aiming to end decades of bloodshed.

The seven countries of the East African Community (EAC), which Congo joined this year, agreed in April to set up a joint force to fight militia groups in Congo's east. The Kenyan troops will join a contingent from Burundi.

Despite billions of dollars spent on one of the United Nation's largest peacekeeping forces, more than 120 armed groups continue to operate across large swathes of east Congo, including the M23 rebels, which Congo has repeatedly accused Rwanda of supporting. Kigali denies the claims.

Uganda has already sent troops into Congo as part of separate deployment to chase down an Islamic State-linked armed militants, one of the warring groups in eastern Congo.

"We all have a stake in a stable Democratic Republic of Congo and its security," Ruto said at a send-off ceremony for the troops in Kenya's capital Nairobi.

Ruto said the United Nations and African Union had given "tacit" backing to the Kenyan deployment.

U.N. spokesman Stephane Dujarric told Reuters Secretary-General Antonio Guterres was not a mandating authority, and that decisions on whether or not to finance such missions were out of his purview.

A U.N. source told Reuters there has been some uncertainty around Kenya's deployment because Nairobi wanted international funding, which requires an official mandate from the U.N. Security Council or the African Union.

"We have been working very hard to mobilise the international community to support the east African force," Kenyan Defence Minister Aden Duale said at the event.

On Wednesday morning several thousand people held a demonstration in the city of Bukavu, eastern Congo, against the regional force because, they said, some of their "enemies" are member countries of the East African Community.