The head of the World Health Organization said on Wednesday that Eritrean troops "murdered" his uncle in the Tigray region of Ethiopia.
Eritrean Information Minister Yemane Gebremeskel did not respond to requests for comment on the allegations.
WHO Director-General Tedros Adhanom Ghebreyesus, a former Ethiopian minister who comes from Tigray, has previously been a vocal critic of Ethopia's role in the conflict that has killed tens of thousands and displaced millions.
In the closing minutes of a Geneva press briefing focused on COVID-19, Tedros said that he nearly cancelled the event because he was "not in good shape" after hearing of his uncle's "murder".
"I hope that this (peace) agreement will hold and this madness will stop but it's a very difficult moment for me," Tedros told reporters, adding that more than 50 other people had been killed in the same incident. The Ethiopian government and regional forces from Tigray agreed in November to cease hostilities last month in a major breakthrough.
However, troops from Eritrea, to the north, and forces from the neighbouring Ethiopian region of Amhara, to the south, who fought alongside Ethiopia's military in Tigray were not party to the ceasefire.
Witnesses and aid workers in the northern region told Reuters that despite the truce Eritrean forces have been looting towns, arresting and killing civilians in the towns they still control across the region.
Ethiopia's government spokesman Legesse Tulu, military spokesman Colonel Getnet Adane, and Prime Minister Abiy Ahmed's spokeswoman Billene Seyoum did not immediately respond to a request for comment on Tedros' remarks.
Asked for details of the incident on the sidelines of the event, Tedros said that his younger uncle whom he grew up with had been killed by Eritrean soldiers in a village in Tigray. He declined to give the location because he said he feared the village would face retaliation.
That followed the killing of his cousin last year in Tigray when a church was blown up, he said, without giving further details.
The Ethopian government, which opposed Tedros' second term as head of the global health agency, has accused him of trying to procure arms and diplomatic backing for rebel forces - charges he has denied.
(Reporting by Emma Farge; additional reporting by Nairobi newsroom, Editing by William Maclean)