UNITED NATIONS (AP) — The Security Council extended the U.N. peacekeeping mission in eastern Congo for a year on Friday and authorized its Intervention Brigade to keep undertaking offensive operations against armed groups, but it also called for "a clear exit strategy" for the U.N.'s largest force.

The resolution adopted by the council kept the force's ceiling at 19,815 military personnel and 1,441 police until March 31, 2015. It also keeps in place an Intervention Brigade, which has an unprecedented mandate to take offensive military action against rebel groups to help end the east's long-running conflict by neutralizing and disarming the fighters.

The council commended the force, known as MONUSCO, "for the positive impact on peace and stability" in eastern Congo.

At the same time, it strongly condemned armed groups for continuing to destabilize eastern Congo and demanded that they immediately halt all violence. It also warned that rebel fighters abusing human rights, including by attacking civilians, will be held accountable.

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 2013, 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 by beefing up the U.N. force with the Intervention Brigade. The council also authorized the use of unarmed drones on a trial basis for intelligence gathering in eastern Congo.

Since then, forces from the government and MONUSCO including the Intervention Brigade have defeated one of the main rebel groups, the M23, who launched a rebellion in April 2012 becoming the latest reincarnation of a Tutsi rebel group dissatisfied with the Congolese government.

France's U.N. Ambassador Gerard Araud said the next step is to neutralize the other armed groups.

The council identified key armed groups still operating in the region as the FDLR, which was formed by extremist Rwandan Hutus who took part in the 1994 genocide and then fled across the border; the Uganda-based Allied Democratic Forces or ADF; the notorious Lord's Resistance Army; the Bakata-Katanga which is fighting for independence for mineral-rich southeast Katanga province; and various Mai Mai groups.

The council noted "with deep concern" reports that the FDLR is collaborating with Congolese army soldiers at a local level and stressed the need for the government, supported by MONUSCO, to start implementing plans "to neutralize the FDLR."

Araud added that if military successes are "to be solid and sustainable" the government must now start improving life for civilians in eastern Congo by expanding state institutions to the region.