Burundi has accused neighbouring Rwanda of training rebels seeking to destabilise the country.
It is hosting Burundi’s failed coup leader, and helping rebels launch cross-border attacks, Foreign Minister Alain Nyamitwe told the BBC.
Rwanda denies the allegation, and says Burundi is trying to deflect attention from its own problems.
The two governments have a tense relationship, with both countries sharing a similar ethnic make-up.
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Burundi has been hit by a spate of assassinations and attempted assassinations since President Pierre Nkurunziza won disputed elections in July.
He survived a coup attempt in March. It was led by renegade Gen Godefroid Niyombare, who opposed his bid for a third term.
Gen Niyombare has not been seen in public since then.
About 70,000 Burundians are living in refugee camps in Rwanda after fleeing the unrest.
Mr Nyamitwe told the BBC Kinyarwanda service that Rwanda was “facilitating” attacks that the coup plotters were orchestrating in Burundi.
“We also have extensive information about recruitments in refugee camps, especially in Mahama refugee camp, where refugees are taken for military training, and some of the trainers are Rwandans,” he added.
On Tuesday, Rwanda’s foreign ministry official Olivier Nduhungirehe accused Burundi of harbouring rebels from the Democratic Forces for the Liberation of Rwanda (FDLR) group, which was linked to the 1994 genocide in Rwanda.
Mr Nyamitwe said a fact-finding team, sent to Burundi by regional leaders, found there was no truth to the allegation.
The team visited Burundi after Rwanda made similar allegations in the past, he added.
Both Rwanda and Burundi have long experienced ethnic conflict between a Hutu majority and a Tutsi minority which has traditionally been dominant.
Rwanda sees the mainly Hutu FDLR as a major threat to its stability, and is pushing for its disarmament.
Mr Nkurunziza is a Hutu former rebel leader, while his Rwandan counterpart Paul Kagame is a Tutsi.
However, the unrest in Burundi is not linked to ethnic divisions, analysts say, and the two presidents used to enjoy good relations, even playing football together.