Julien Mpaluku, the provincial governor of the North Kivu district, said on Thursday that Rwandan soldiers crossed into Congo three days ago and headed for the frontier villages of Tshanzu and Bunagana.
He said Rwandan troops were fighting in Rumangabo, a small village north of the regional capital, Goma.
Antipas Mbusa Nyamwisi, the Congolese foreign minister, repeated the charge to the Reuters news agency.
Village attacked
"The Rwandans are indeed there. They now want to take Goma," Nyamwisi was reported as saying.
The accusations follow a series of attacks on Congolese troops by Tutsi fighters led by Laurent Nkunda, a renegade army general, in the border province of North Kivu.
Rwanda's mainly Tutsi government is said to be supportive of Nkunda.
Congolese army tanks fired into the hills at fighters, who took control of a military base in the village of Rumangabo, about 40km north of Goma, on Wednesday.
The fighting forced wildlife rangers to evacuate their headquarters in the southern sector of Virunga National Park, home to some of the last remaining mountain gorillas on earth, Samantha Newport, a park spokewoman, said.
Rwandan rejection
The UN, which has its biggest international peacekeeping force deployed in the Democratic Republic of Congo, urged both sides to respect and support existing peace processes that have sought to end the fighting in Congo's east.
Asked about the Congolese allegations, Michel Bonnardeaux, a spokesman for the UN Congo mission (Monuc), said: "We are aware of collusion allegations from both sides and that's why we insist on bringing the parties back to the table to repair trust and restore confidence in the peace process."
Rejecting the Congolese allegations, Richard Sezibera, Rwanda's ambassador to the Congolese Great Lakes region, said: "There are UN Monuc troops in those areas. If Rwandan troops were there, would not the whole world know by now?"
Rwanda has invaded Congo in the past, including a major invasion in a 1998-2003 war that sucked in neighbouring states.