The top U.N. envoy in Congo said Monday there are "credible reports" that the M23 rebel group is recruiting fighters and resuming activities despite last month's peace agreement with the Congolese government following its military defeat.

Martin Kobler told the U.N. Security Council that the M23 must not be allowed to re-emerge as a military force, which would roll back regional and international efforts to end decades of fighting centered in mineral-rich eastern Congo.

M23 launched its rebellion in April 2012, becoming the latest reincarnation of a Tutsi rebel group dissatisfied with the Congolese government. Rwanda's Tutsi-led government has been accused by U.N. experts and others of backing the M23 and using it as a proxy force to secure access to eastern Congo's lucrative mining trade — an allegation the government denies.

The December peace agreement between the M23 and Congo's government, which was signed in Nairobi, requires the insurgent group to demobilize its fighters and transform itself into a political party.

In the past month, however, Kobler said, "there are credible reports that the military recruitment of the M23 did not cease ... (and) of emerging M23 activities in Ituri in northeastern Congo."

He urged Congo's government to implement the agreement with M23 and expedite the disarmament, demobilization and reintegration of its fighters, a process he said "is still too slow."

Kobler also urged the Rwandan and Ugandan governments "to do everything possible to prevent M23 elements from sheltering or training troops on their territory."

The Congo conflict is a spillover from the 1994 genocide in neighboring Rwanda. Hundreds of Hutus who participated in the mass slaughter escaped into Congo and still fight there, along with other armed groups.

In February, the Congolese government and 10 other African nations including Rwanda and Uganda took the most concerted action to bring peace to Congo by signing an agreement not to interfere in each other's internal affairs or host armed groups.

The Security Council followed up in late March by beefing up the U.N. peacekeeping force in Congo with an "intervention brigade" and giving it an unprecedented mandate to take offensive military action against rebel groups to help bring peace to the east by neutralizing and disarming their fighters. The council also authorized the use of unarmed drones on a trial basis for intelligence gathering in eastern Congo.

Mary Robinson, the U.N. envoy for the Great Lakes region of central Africa, told the council by videoconference from the Congolese capital, Kinshasa, that the positive atmosphere following the December peace agreement between Congo and the M23 "has vanished."

"The region is going through a period of renewed turbulence," she said, pointing to an attack on Dec. 25 by ADF rebels on the town of Kamango that killed more than 50 people and coordinated attacks on Dec. 30 in Kinshasa, Lumbumbashi and Kindu that left more than 100 people dead.

Robinson urged all parties to the February agreement to immediately implement all commitments "in order to bring about concrete peace dividends and lasting life improvement to the people in the region."

With the defeat of M23, he said, U.N. and Congolese forces are now focused on defeating the Democratic Forces for the Liberation of Rwanda, or FDLR, which was formed by extremist Hutus from neighboring Rwanda who took part in that country's 1994 genocide and then fled across the border.

Kobler said first operations against FDLR "have cleared some positions." He urged the Congolese forces "to intensify the joint planning and execution of operations against the FDLR."

Kobler said Congolese and U.N. forces will also be going after the ADF, a group of Islamist rebel fighters led by Ugandan commanders, this year.