Congo's M23 rebels clashed with government troops on Friday near the eastern city of Goma, a rebel leaders said, in the first heavy fighting in nearly two months.
General Sultani Makenga, M23's military commander, told Reuters its forces were attacked at 4 a.m. local time (2200 ET) at Kanyamohoro, around 15 km (10 miles) north of Goma, the largest city in eastern Democratic Republic of Congo.
"They attacked us," Makenga told Reuters by telephone. "We are going to defend our positions."
An army spokesman was not immediately available for comment.
A Reuters reporter in Goma said the fighting was intense and on-going.
The resumption of hostilities comes days after peace negotiations broke down in the Ugandan capital Kampala, triggering a military build-up on both sides.
The government said the talks stalled when it refused to grant M23's demand for amnesty for its leaders and reintegration into the army. M23 says it has no desire to rejoin the Congolese forces.
This is the second time in three months that peace talks have stuttered and combat has broken out between the army and the 20-month-old rebel movement.
In late August, government troops with the support of a new U.N. Intervention Brigade forced M23 from its positions just north of Goma.
M23 began as a mutiny by Congolese soldiers in early 2012. The rebels demand that the government fully implement the terms of a 2009 peace deal signed with a previous rebellion which was backed by Rwanda.
United Nations investigators have accused Rwanda of supporting M23, charges that Kigali has strenuously denied.
(Reporting by Kenny Katombe in Goma and Pete Jones in Kinshasa; Editing by Daniel Flynn)