UNITED NATIONS (AP) — Congolese troops supported by U.N. peacekeepers have neutralized about 25 percent of a rebel group in northeast Congo — but joint operations against the larger FDLR military group remain at a standstill, the top U.N. envoy in Congo said Tuesday.

Martin Kobler told the U.N. Security Council that the success of the joint operation against the Ituri Patriotic Resistance Force, also known as FRPI, since June 3 has shown what can be achieved when the Congolese army and the U.N. force work together.

He said the ongoing operations against FRPI in the northeastern Ituri region are the most effective since the M23 rebel group was toppled in 2013.

Ituri has seen a resurgence in violence in recent months following the arrest of FRPI leader Cobra Matata in January. FRPI is one of many militias that have fought in Ituri for a stake in the region's rich natural resources, including gold, diamonds and copper.

Last year, Kobler said the end of the FDLR would be "a turning point" that would fundamentally alter the security situation in eastern Congo, where armed groups have wreaked havoc for years. The FDLR was formed by extremist Rwandan Hutus who fled into eastern Congo after taking part in the 1994 genocide in Rwanda.

The U.N. had hoped to be part of a joint operation against the FDLR, but in February it formally ended its support for a Congolese military offensive after the government picked two generals linked to human rights violations to lead the operation. Those generals remain in command and the Congolese military is pursuing the FDLR on its own.

Kobler said despite the army's progress in dislodging the FDLR from some strongholds in the east, it is facing difficulties in consolidating its hold in liberated areas.

"Today, the FDLR is returning to some of its previous strongholds," he said, and insecurity is on the rise again with targeted killings, rapes, armed robberies and abductions for ransom becoming more common.

Kobler said "the paralysis of anti-FDLR operations has cascaded into other fields" including in the eastern area of Beni where rebels from the Uganda-based Allied Democratic Forces, or ADF, continue "to instill fear in the hearts of a defenseless population." He stressed the importance of not underestimating "the Islamist nature of the ADF."