Democratic Republic of Congo’s government said on Friday it was ready to launch military operations against Rwandan Hutu rebels in its east after most missed a deadline to disarm and return home or go into exile.

A six-month ultimatum set by regional leaders expires at midnight and just 300 of the estimated 1,5000 rebels have disarmed, according to Congo’s government.

The fighters, known as the FDLR, include some of the remnants of the Hutu militia that took part in the 1994 genocide and have been at the heart of two decades of violence in Congo’s mineral-rich east since then. The same rebels who helped the Congolese forces to wipe off the M23

“The option of disarming (the rebels) by force is now inevitable and all the preparations to do so have been made,” the government said in a statement read on state television.

The statement did not give any further details but the rebels operate in North and South Kivu provinces, which lie on Congo’s border with Rwanda and Burundi.

If an assault goes ahead, Congo’s government will rely heavily on the U.N. peacekeeping mission, known as MONUSCO, and its Force Intervention Brigade, a beefed up unit within the mission that has the mandate to hunt down rebels.

The 3,000-strong brigade recorded significant successes in 2013 when it helped Congolese forces defeat Tutsi-led M23 rebels who had seized swathes of North Kivu, with the support of Rwanda, according to U.N. experts.

However, the prospects of an immediate and quick operation against the FDLR are complicated by rivalries between the various regional powers involved, the rugged terrain the rebels occupy and their past history of striking civilians in revenge when attacked.

The U.N. mission is also stretched trying to track down members of the Ugandan ADF-NALU rebel group that has been accused of killing dozens in eastern Congo in recent weeks.

Nonetheless, international envoys for the Great Lakes region called on Friday for immediate action, saying the lack of voluntary disarmament left no alternative to the military option and FDLR fighters must now be neutralized.

Rwanda said the rebels had taken advantage of the disarmament window to consolidate their positions and regional leaders must now follow through on their threats.

“The delaying tactics and excuses that have allowed the FDLR to perpetuate their crimes and genocidal ideology should no longer be tolerated,” it said in a statement.

FDLR leaders have called for talks with Rwanda but Kigali has repeatedly rejected the demands, accusing them of wanting to complete the slaughter of Tutsis and moderate Hutus that claimed 800,000 lives 20 years ago.