Regional authorities in the eastern Democratic Republic of Congo said Rwandan soldiers and artillery supported attacks by the M 23 rebel group on Sunday, accusing Rwanda of trying to occupy the Congolese border town of Bunagana.
The violence forced over 25,000 people to flee the area, with thousands escaping to neighbouring Uganda, the UN humanitarian agency OCHA said.
The accusations of Congo is part of an escalating dispute between the neighbours that has revived old animosities. Rwanda denies backing the M 23 offensive.
The office of the governor of North Kivu province said that Congolese forces had repelled early-morning attacks by M 23 backed by Rwandan forces, near Bunagana and elsewhere.
The goal of Rwanda is to occupy Bunagana in order not only to asphyxiate the city of Goma but also to put pressure on the Congolese government, it said in a statement.
The Rwandan government could not be reached for comment. It denies playing any role in M 23's recent attacks, but has echoed M 23 charges that Congo is cooperating with the Democratic Forces for the Liberation of Rwanda FDLR an armed group run by ethnic Hutus who fled Rwanda after taking part in the 1994 genocide.
On Thursday, Congo accused Rwanda of sending 500 commandos in disguise into eastern Congo.
The countries accused each other of firing rockets across their shared border on Friday. Two Congolese children were killed by a strike, according to Congo's army.