Burundi accused neighboring Rwanda on Monday of supporting a rebel group that was recruiting Burundian refugees on Rwandan soil, allegations Kigali denied.

 The comments were prompted by a report published by the charity Refugees International, which said it was “deeply concerned” by claims of Burundian refugees in Rwanda that they were being recruited by “non-state armed groups“.

It is the latest sign of tension between the African neighbours, which each have an ethnic Hutu majority and Tutsi minority. Both have also been torn apart by ethnic conflict in the past and experts fear months of violence during a political crisis in Burundi may reopen old ethnic wounds.

More than 220,000 have fled Burundi since the crisis erupted in April, sparked by President Pierre Nkurunziza’s bid for a third term. He was re-elected in a disputed July vote. Rwanda says more than 73,000 Burundians are now on its soil.

“We have been emphasising the fact that Burundi refugees are recruited into a rebel group, trained and armed by Rwanda.

Burundi continues to condemn and denounce it,” Burundi’s presidential media adviser, Willy Nyamitwe, told Reuters.

He said armed insurgents, led by officers who launched a failed coup, had attacked Burundi in July and “found refuge in Rwanda.” He said the group “continued to perpetrate terrorist attacks in Burundi,” he wrote in a message via social media.

A trial began in Burundi on Monday of some of those behind the failed coup in May.

No explanations were offered as to why Rwanda, scene of a genocide in which 800,000 mostly Tutsis as well moderate Hutus were massacred, would want to support a rebel group against Burundi.

Rwanda’s minister of disaster management and refugee affairs, Seraphine Mukantabana, dismissed the allegations when asked about the report by Refugees International.

“These are continuing baseless allegations,” she said, dismissing the idea of any refugees going missing because of any recruitment. “Even some few refugees who return home respect all legal requirements,” she said.

The minister could not immediately be reached to respond specifically to Nyamitwe’s remarks, but the Rwandan government has dismissed similar accusations in the past.

Refugees International, which cited interviews with groups refugees for its recruitment claim, called on Rwanda and Burundi to respect the “humanitarian character of asylum” and protect refugees from being recruited by “non-state armed actors“.

Rwanda has enjoyed international praise for rebuilding its economy after the 1994 genocide. Burundi, which is far poorer, has been in turmoil for months after a decade of relative calm since a 12-year civil war ended in 2005