UN leader Ban Ki-moon renewed claims Tuesday that rebels in eastern Democratic Republic of Congo have had "external support" and warned that conflict could erupt again.
Ban's latest report on DR Congo to the UN Security Council did not single out any country for backing the M23 rebels, who briefly seized the main eastern city of Goma in November.
But UN experts have said the rebels were aided by Rwanda and Uganda, and Ban said the group conscripted child soldiers in Rwanda. Both countries have strongly denied involvement in the uprising against the DR Congo government.
Government soldiers and troops from the UN mission, MONUSCO, held back M23's first attack on Goma, and Ban said the group's second attempt showed clear evidence of outside help.
"The subsequent speed, efficiency and success of the renewed M23 offensive were rendered possible by a sudden increase in the group's combatants, coordinated multi-pronged attacks, and attacks with coordination between infantry and fire support."
These were "capacities" that the rebels were not known to have.
UN "observations of the command and control ability of the attacking force, the effective coordination of its fire support, the quality of its equipment and its general fighting ability, particularly during nighttime, all suggested the existence of external support, both direct and indirect," added the report.
There is currently a tense ceasefire in eastern DR Congo while the UN prepares plans to beef up its peacekeeping mission. Ban hopes to sign a regional political deal to end the turmoil later this month.
He warned, however, that "the possibility of a resumption of hostilities remains a serious threat."
UN sanctions experts said in a report to the Security Council in December that hundreds of Rwandan troops had helped M23 with its offensive.
The Security Council has ordered sanctions against rebel leaders accused of orchestrating widespread abuses including mass rapes.
Ban's report said M23 conscripted child soldiers in DR Congo and Rwanda.
"A total of 21 boys, including at least seven Rwandan nationals associated with M23 in North Kivu, were interviewed by MONUSCO," said the report.
"Their testimonies detailed widespread, ongoing and systematic underage recruitment on Congolese and Rwandan territory, as well as other violations, such as the killing and maiming of children within the ranks of M23."
Presidents from DR Congo, Rwanda, Uganda, Burundi, Angola, Congo, South Africa and Tanzania are expected in Addis Ababa on February 24 to sign the UN-brokered accord aimed at ending two decades of conflict in eastern DR Congo.
The presidents will sign a pledge not to interfere in their neighbors' affairs while the UN also plans to deploy a 2,500-strong "intervention brigade" in eastern DR Congo with orders to end the threat from the armed rebels.