The U.N. Security Council urged Congo's president on Thursday to quickly sign a document authorizing a joint U.N.-Congolese military operation against a rebel group that failed to surrender by a Jan. 2 deadline.

A presidential statement approved by all 15 council members reiterated the council's readiness to consider targeted sanctions against those supporting the Democratic Forces for the Liberation of Rwanda.

The rebel group, known as the FDLR, was formed by extremist Rwandan Hutus who took part in the 1994 genocide and then fled across the border into Congo. It now includes Congolese fighters, and the Security Council said it continues to recruit new combatants.

The council statement stepped up pressure on Congo's President Joseph Kabila following his assurance to Secretary-General Ban Ki-moon in a phone call Wednesday that Congo's army is ready to take military action with the U.N. peacekeeping force known as MONUSCO.

The Security Council statement noted a Congolese government statement on Jan. 2 which said military action against the FDLR is now "inevitable."

MONUSCO's Intervention Brigade, which has a mandate to take offensive military action against rebel groups, is expected to spearhead the operation along with regular U.N. peacekeeping troops, according to a senior U.N. official.

The official, who spoke on condition of anonymity because talks were private, said the U.N. expects Kabila's government will sign the joint directive authorizing the operation "very soon" and that military action would start soon afterward.

The military operation could take months because the estimated 1,500 FDLR combatants don't wear uniforms and live with their families in large areas of North Kivu, South Kivu and northern Katanga provinces, mingling with the civilian population, the official said.

Congolese support is critical because once the rebels are defeated Congolese forces need to move in quickly to restore security and the government must start providing services, the official said.

Eastern Congo is home to a myriad of armed groups and militias, many vying for control of the region's vast mineral resources.

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 in Congo with the Intervention Brigade and authorizing the use of unarmed drones on a trial basis for intelligence gathering in the east.

Since then, Congolese forces and U.N. peacekeepers have defeated one of Congo's main rebel groups, the M23.