The United Nations has said it cannot forcibly disarm rebels accused of taking part in Rwanda's genocide amid anger that 25 militiamen it interviewed later escaped with their weapons.
Rwanda has complained bitterly that neither UN troops nor the Congolese are rooting out extremist Hutu rebels, or Interahamwe, who fled to Congo after the 1994 genocide in which 800,000 people died in 100 days of ethnic slaughter.
The latest row centres around 25 Rwandan rebels detained in the Congo who later escaped after being interviewed by UN officials.
"Our position is very clear. We only have a mandate for voluntary disarmament and repatriation," Ms Patria Tome, spokeswoman for the UN mission in Congo, said.
"We did our job and spoke to these people but they did not want to disarm or go back to Rwanda".
The presence of thousands of Rwandan rebels in eastern Congo during the last 10 years has fuelled ongoing regional instability and was specifically used by Kigali as justification for invading Congo in 1996 and 1998.
"It is neither understandable nor acceptable that a UN force that is over 10,000 strong in the Congo and on which the international community spends close to $700 million every year can fail to disarm 25 men," Mr Richard Sezibera, a Rwandan presidential envoy said.
"Rwanda and the entire region have said the international community needs to forcibly disarm these groups, repatriate them, demobilise them and stop their completion of the genocide which they want to carry out," he told Rwandan radio.
Congo's partially reformed army is still weak and remains largely divided as Africa's third largest nation struggles to recover from its own five-year war that killed 3 million people, mostly from hunger and disease.
The army, which has pledged to investigate the affair, has in the past collaborated with the Hutu rebels but denies it still does so.
The UN mission estimates that about 10,000 rebels remain in eastern Congo. For the moment, however, its mandate only allows it to disarm and repatriate combatants that put themselves forward for the process.