The Armed Forces of the Democratic Republic of Congo and the UN accused the M23 rebels Tuesday of violating a cease-fire the group had declared earlier in the day.
The reported breach came within hours after the rebel group said it had declared a cease-fire to pave the way for dialogue with the government.
In a statement, the Congolese military said the rebels attacked several army positions in eastern North Kivu province, which has been the scene of fighting for several months.
"Fighting is ongoing between the army and the M23 even when the group is supposed to respect the latest cease-fire," the statement said.
Separately, the UN also accused the rebel group of ignoring the cease-fire.
"Our peacekeeping mission, MONUSCO, indicated that fighting between the Congolese army and the M23 armed group continues in North Kivu province, despite the cease-fire," said Farhan Haq, deputy spokesman for UN Secretary-General Antonio Guterres.
"The secretary-general reiterates his call on the M23 to respect the cease-fire to create conditions for its full and effective withdrawal from all occupied areas in eastern DRC," Haq said.
"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."
Three people were killed and six more injured Monday in the city of Sake, located 27 kilometers (16.7 miles) from Goma, the capital of North Kivu province, during M23 shelling, according to the Congolese army.
On Monday, clashes were also reported in parts of Rutshuru and Masisi territories.
The cease-fire deal was reached following consultations between the M23 leadership and Angolan President Joao Lourenco held in the capital Luanda as well as decisions made at various regional meetings, the rebels said in a statement earlier Tuesday.
Since last year, fighting between the M23 and government forces has displaced over 600,000 people.
The fighting has heightened tensions between Rwanda and the neighboring Democratic Republic of the Congo's government.
Kinshasa accuses Kigali of backing the rebel group, a charge Rwanda denies.
A cease-fire demanded by African leaders in the Angolan capital of Luanda last November was also broken within days.
