This was the first time in more than two months that Mr Debretsion had spoken in public. An audio recording of his comments, lasting for about 20 minutes, was broadcast on a Facebook account run by a TPLF media outlet.
"A devastating and genocidal war was waged against the people of Tigray because they firmly fought for their right to self-determination and they held a democratic election. The invasion and massacre has continued. So does the struggle of the people of Tigray," he said.
Mr Debretsion also alleged widespread incidents of murder, rape, torture and starvation.
It is unclear when the recording was made but he mentioned the killings of other TPLF leaders, which suggested it was recent.
Mr Debretsion is wanted by the government on charges of treason.