Yet Kinshasa also said Rwanda had not responded to its calls to extradite Congolese Tutsi rebel leader Laurent Nkunda, whose arrest in Rwanda was seen as part of the agreement that allowed Kigali, a former occupying force, to send troops back to Congo.
The fighting is the first reported clash the joint force has had with the Rwandan Hutu FDLR rebels since Kinshasa let in more than 3,500 Rwandan soldiers this week to hunt for the rebels, some of whom took part in Rwanda's 1994 genocide.
General John Numbi, the Congolese commander of eastern operations, reported fighting with the FDLR in five villages on Friday and Saturday. "On the side of the FDLR, nine elements were killed," he said in a statement on Saturday.
One Congolese soldier had been wounded, Numbi said.
Nkunda rejected peace deals that ended Congo's 1998-2003 war, which killed five million people and saw Rwanda back anti-Kinshasa rebels, leading a five year rebellion instead.
The United States said his arrest on Thursday in Rwanda was a "step on the road to peace" but it has been met with both relief and doubts amongst Congolese civilians.
Nkunda and his fighters are accused of mass killings, rapes and the recruitment of child soldiers. International Criminal Court prosecutors have a war crimes arrest warrant for Bosco Ntaganda, Nkunda's deputy who led a split with Nkunda.
The ICC has declined to say whether Nkunda would be prosecuted but Congo was quick to call for his extradition from Rwanda, which U.N. experts said backed Nkunda as recently as last year.
"We are waiting for the Rwandans to contact us on this," Congolese Information Minister Lambert Mende said on Saturday.
Analysts say bringing Nkunda back to Congo for trial could help Kabila sell the joint force agreement to a population still wary of Rwandan intervention after years of occupation that brought accusations of plundering.
One Western diplomat told Reuters on Saturday the Rwandans might be trying to backtrack on the agreement now. Rwandan officials may fear a trial will expose the country's links to Nkunda or complicate the ongoing military operations, he said.
Reactions to Nkunda's arrest have been mixed on the ground.
"I heard it (Nkunda's arrest) on the radio. But I haven't seen him yet, and I don't know if it is true," said Bagambe Rushago, who now lives in a sprawling city of banana leaf huts which sprang up during Nkunda's advance on Goma last year.
"I hope it's true. That would be a good thing," he added.
After numerous false dawns, including 2006 polls which were meant to usher in an era of peace after Congo's last war and amid uncertainty over Nkunda's fate, others are more doubtful.
"I'm not sure it will end the war. As long as the people who supported him are still there, a new Nkunda could still be born," said Innocent Gasigwa, another camp resident.