(Bloomberg) -- The M23 rebel group clashed with Democratic Republic of Congo soldiers, defying a ceasefire that was meant to go into effect Tuesday, according to the United Nations.

“The secretary-general reiterates his call on the M23 to respect the ceasefire to create conditions for its full and effective withdrawal from all occupied areas,” Farhan Haq, deputy spokesman, said in comments published on the UN’s website. “He condemns all violence against civilians and renews his call on all Congolese and foreign armed groups to lay down their weapons and disarm unconditionally.”

The rebel group fighting in eastern Congo had agreed to an immediate ceasefire as part of an effort by regional leaders to end a conflict that threatens to ignite a war between Congo and neighboring Rwanda. 

Congo accuses Rwanda of supporting the M23, which says it’s protecting the rights of Congolese of Rwandan heritage. An offensive by the rebels that advanced toward the trading hub of Goma displaced more than 600,000 people since last March, according to the UN. 

The ceasefire was part of an agreement brokered by Angolan President Joao Lourenco, M23 said in a statement on Tuesday. The group said it still reserved “the full right to defend itself” if attacked by Congo’s army or other armed groups. A previous pact accepted in November failed within days. 

Congolese President Felix Tshisekedi has campaigned for sanctions against Rwanda, which continues to deny backing the rebels despite a report by United Nations experts. Rwanda supported a previous offensive by the M23 that was defeated by Congo’s army and UN peacekeepers in 2013.

Conflict in mineral-rich eastern Congo began in the 1990s in the aftermath of the civil war and genocide in Rwanda. Today more than 100 armed groups are active in the region, with nearly 7 million people displaced due to violence, according to the UN. Congo is the world’s biggest producer of cobalt, while the region is rich in gold, tantalum and other resources.

Lourenco and ex-Kenyan President Uhuru Kenyatta are leading the peace talks while troops from the East African Community have been deployed to help stem the violence. 

On Monday, UN Secretary General Antonio Guterres called on the M23 to begin withdrawing from the areas it occupies in eastern Congo.

Those who don’t respect the peace process can expect to be sanctioned, French President Emmanuel Macron said during a visit to Congo’s capital, Kinshasa, over the weekend.

(Recasts with clashes continuing from first paragraph)

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