Autopsies on five bodies returned by Rwanda to the Democratic Republic of Congo show they were probably executed, a military source has told the BBC.
The bodies were handed over following border clashes between the two countries armies earlier this month.
DR Congo says they began when a corporal was kidnapped by Rwandan soldiers who crossed the border.
Rwanda says the men were killed in combat after they attacked Rwandan soldiers on its territory.
The neighbours have had a fractious relationship since the 1994 Rwandan genocide, when those accused of involvement in the killings of an estimated 800,000 ethnic Tutsis and moderate Hutus set up a militia in eastern DR Congo.
The autopsy report concluded that the five men who were returned to DR Congo after the clashes had wounds to the head – two inflicted by a sharp object, three by bullets.
It also found that all of the men had been shot several times in other parts of the body, including the thorax and the abdomen, and at close range. One of the men had been shot eight times in the back.
Earlier, DR Congo’s Information Minister Lambert Mende said it was clear from the photographs that the five men, one of whom he says was a Congolese soldier, were executed.
Rwanda’s government said the five were Congolese soldiers who engaged in a fire fight with Rwandan troops in Rwanda’s Busasamana district and that it did not know the exact circumstances of their deaths.
Rwandan Foreign Minister Louise Mushikiwabo said she was waiting for a regional group of experts – mandated to monitor events on the border – to deliver its investigation into the incident.
The experts’ report, says that at the two sites where Rwanda said the Congolese men were killed in combat, no traces of empty cartridges were found.
The report, which was not signed by Rwanda, also includes a Google Earth map showing that the hill at the centre of the dispute – which Rwanda says is in its territory – is inside DR Congo.
The Rwandan military said the report was misleading and added that Google Earth was not a credible reference for border demarcation.
Rwanda has been accused by the UN of playing a part in the unrest in eastern DR Congo over the years, a charge it denies.
Most recently it was accused of backing a rebellion by the M23 – a mainly ethnic Tutsi movement, which was defeated by the Congolese military and a special UN brigade in November.
In May, the FDLR rebel group – formed by Hutu militiamen accused of involvement in the 1994 genocide – began a disarmament process.
More than 100 of its fighters surrendered to the UN for repatriation to Rwanda – though no military or political leaders from the 1,500-strong group were amongst them.