Rwanda has criticised the Democratic Republic of Congo for halting military operations against Hutu rebels who fled there after the 1994 Rwandan genocide.
The FDLR want security guarantees before returning to Rwanda
Rwanda's foreign minister told the BBC the rebels were attempting to gather strength in eastern DR Congo to launch attacks on his country.
Earlier this week, DR Congo said it stopped the seven-month offensive to avoid further bloodshed.
The UN says more than 160,000 people have been displaced by fighting.
The Tutsi-led government in Rwanda has twice invaded DR Congo, saying it wants to wipe out the Democratic Liberation Forces of Rwanda (FDLR).
They include members of Rwanda's former army and extremist Hutu militia, the Interahamwe, who led the 100-day genocide where 800,000 Tutsis and moderate Hutus were killed.
The Congolese army and UN peacekeepers had been carrying out joint operations in the area against the fighters since January.
Rwanda's foreign minister says by stopping their military offensive, DR Congo showed it lacked the will to deal with the Hutu forces.
"These ex-Interahamwe have been looting, maiming, raping, killing the Congolese people in the hope that they will gather enough strength to come to Rwanda and finish a genocide they were unable to finish in 1994," Charles Murigande told the BBC's Network Africa programme.
"I would not imagine that a serious government can contemplate living with people who are responsible for such horrible crimes."
He said he could not understand why the Congolese government would not accept Rwanda's offer of troops to help deal with the rebels.
"In the past, we offered to mount joint operations against the Interahame. We offered to put our forces under the command of DRC commanders... but this offer has not been accepted," he said.
But Mr Murigande said Rwanda would deal with the issue through dialogue and he was about to travel to Kinshasa for talks.
The presence of Hutu forces in the east has also led to tensions between DR Congo's own Hutu and Tutsi population.
Earlier this year, Tutsi units in the Congolese army, led by the controversial Gen Laurent Nkunda, started a major offensive to try to wipe out an estimated 6,000 Hutu rebels.
Several villages where the Hutu rebels had set up bases were stormed by the army.
But this also displaced more than 160,000 civilians and instead of laying down their arms, many of the Hutu rebels simply fled further into the bush.
DR Congo's government says its priority should now be peace, development and the creation of a strong united army, rather than creating further instability.
The rebels have repeatedly said they do not want to go back to Rwanda unless they are granted amnesty.
Last year's historic elections were supposed to mark the end of years of conflict and mismanagement in DR Congo.