UNITED NATIONS (AP) -- The U.N. envoy to Congo warned Friday that large-scale conflict could erupt again without warning as 11 nations prepare to sign a peace agreement aimed at ending nearly two decades of unending fighting in the mineral-rich African nation.

Roger Meece told the U.N. Security Council that the security situation in the eastern Congo continues to deteriorate amid increasing fears that the rebel group known as M23, which captured the key city of Goma in November, will resume major military action imminently. He also warned of a new hotspot in southern Katanga where an alarming increase in militia activity has displaced 316,000 people.

Meece urged the Security Council to support and quickly deploy a new fighting force which would be part of the U.N. peacekeeping mission to help counter the rebels and bring peace to the country.

"The overall situation is volatile and precarious, and could break down at any time into large-scale conflict without much if any prior warning,'' Meece said.

His grim assessment came two days before a signing ceremony in Addis Ababa, Ethiopia, where Congo and 10 other African nations are expected to sign an agreement aimed at getting key nations to help end the violence.

U.N. Secretary-General Ban Ki-moon left New York Friday to attend Sunday's ceremony where the U.N. will serve as one of the guarantors of an agreement to be signed by Congo, Angola, Burundi, Central African Republic, Republic of Congo, Rwanda, South Africa, South Sudan, Tanzania, Uganda, and Zambia, U.N. spokesman Martin Nesirky said.

Eastern Congo has been engulfed in fighting since the 1994 Rwanda genocide. The United Nations has more than 17,700 U.N. peacekeepers and over 1,400 international police in Congo, a sprawling nation the size of Western Europe. U.N. soldiers were "substantially engaged militarily to oppose M23 offensive operations,'' Meece said, but they were unable to protect civilians as the rebels swept through eastern Congo last year and seized Goma.

Meece said the U.N. mission has operated for years as a traditional peacekeeping operation for a post-conflict environment, but as recent events have underscored again, its troops are repeatedly called on to deal with active conflict, and that's why "an additional military force or brigade'' is essential to help enforce peace.

Security Council diplomats, speaking on condition of anonymity because talks have been private, say the council is likely to approve a new military force, probably a brigade, with troops likely coming from southern Africa.

Meece said that while M23 troops pulled out of North Kivu's capital, Goma, under international pressure, they continue to conduct patrols and stage operations immediately adjacent to the city. They also continue to consolidate their administration in areas of North Kivu they still occupy, and continue to recruit new combatants, including minors, sometimes using force, he said.

The U.N. mission has also seen an increase in activity by other Congolese militias in North Kivu, which is contributing "to a general situation of instability.''

Meece stressed that U.N. forces and resources "are stretched very thin'' and peacekeepers have been able to respond in only a very limited way to new threats in eastern Maniema province and Katanga where a leader of the Mayi Mayi militia known as Gedeon, who escaped from prison in late 2011, has led stepped-up military activity.