The U.N. Security Council warned Friday of military action if a rebel group with some 1,500 fighters in eastern Congo doesn't lay down its arms and surrender by a January deadline.

A press statement from the council noted with "deep concern" that since the deadline was set in early July, no member of the Democratic Forces for the Liberation of Rwanda, an armed group otherwise known as the FDLR, has voluntarily surrendered. The group was formed by extremist Rwandan Hutus who took part in the 1994 genocide and then fled across the border.

The council is calling on Congo, with the support of the U.N. mission there, to "undertake military action against those leaders and members of the FDLR who do not engage in the demobilization process or who continue to carry out human rights abuses."

The statement follows the U.N. secretary-general's latest report on Congo, which calls the disarmament of the FDLR "stalled."

The same report, which was released last week, indicated that this was not the first time that a disarmament demand was ignored. A joint delegation that included Congo and the U.N. mission in August delivered "a strong message" to the FDLR leadership saying 70 percent of its fighters should disarm and leave the country by Oct. 2.

As of August, an estimated 1,500 rebels remained active.

Eastern Congo is home to a number of armed groups and militias, many competing for control of the region's vast mineral resources. While the fighting is mainly a spillover from Rwanda, it also includes rebel groups from Burundi and Uganda.

In August, the top U.N. envoy in Congo said security in the east has vastly improved in the last year, but the situation remains fragile. Martin Kobler told the Security Council that the key to peace is to disarm the FDLR's remaining fighters.

The new Security Council statement rejects "any call for political dialogue with the FDLR" and repeats the demand for those responsible for genocide, war crimes and crimes against humanity to be arrested and brought to justice.

In February 2013, the Congolese government and 10 other African nations, including Rwanda, 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 strengthened the U.N. force with an Intervention Brigade, which has an unprecedented mandate to take offensive military action against rebel groups.

Since then, Congo and U.N. forces have defeated one of the main rebel groups, the Congolese Revolutionary Army, or M23, and turned their attention to the others like the FDLR.