A government delegation has gone to eastern Democratic Republic of Congo to try to halt an outbreak of fighting.
The renegade soldiers have control of the dusty, deserted streets
More than 20,000 people in the small town of Kanyabayonga, now controlled by dissident Congolese troops, have fled fierce clashes between rival factions.
Interior Minister Theophile Mbemba said the mediation team wanted to establish the motives of the fighters.
In a BBC interview, Rwandan President Paul Kagame has again denied deploying soldiers inside Congo.
Mr Kagame added that Rwanda had no involvement in the fighting in Kanyabayonga, despite COngolese government claims.
The Congolese war officially ended in 2002 after some three million deaths.
This fighting raises fears that the war, which drew in at least six other African armies, could reignite.
The United Nations said it had repulsed an attempt by armed men to cross from Rwanda into DR Congo in three dug-out canoes, near Bukavu, to the south of Kanyabayonga.
A spokesman said the boats turned round after an exchange of fire.
Kanyabayonga's inhabitants have fled alongside the defeated forces of the Congolese government, reports the BBC's Arnaud Zajtman from the town.
He says pro-Rwandan soldiers are deployed in the town and have also set up camps on the surrounding mountains, 160km (100 miles) north of the North Kivu provincial capital, Goma.
This allows them to monitor the movement of government troops near the frontline, some 8km north.
Captain Kabakuli Kennedy, who is in control of the town, says he is a former Congolese rebel who received support from Rwanda during the war, but that he is now fighting without any external support.
He says he is protecting the rights of the Congolese minority who speak Kinyarwanda, the language also spoken in Rwanda.
Military and government officials said two Rwandan soldiers had been captured in the fighting in Kanyabayonga. Each side also allege they have killed at least a dozen enemy soldiers, but neither figure can be verified.
There have been many recent reports that Rwandan troops crossed the border but the UN said last week that there was no conclusive evidence.
A mission of UN peacekeepers is going to investigate the fighting.
Rwanda has denied there are any Rwandan forces in DR Congo.
However, confidential UN documents seen by the BBC and made public last week said Rwanda retained a "Rwandan military structure of control" over parts of DR Congo through the use of proxy Congolese forces.
Under the power-sharing agreement set up to end the five-year war, North Kivu was awarded to the former RCD rebels backed by Rwanda, who are supposed to have been integrated into the national army.
Some reports suggest these soldiers mutinied and were fighting the regular Congolese army.
The situation in eastern DR Congo is extremely complex, with many rival armed groups and very little control from central government.
Rwanda has threatened to send troops into DR Congo to hunt down the ethnic Hutu rebels accused of carrying out the 1994 genocide.