World Health Organization Director-General Tedros Adhanom Ghebreyesus said on Wednesday there was a "very narrow window now to prevent genocide" in his home region of Tigray in northern Ethiopia.
Tedros, who previously served as Ethiopia's health minister and foreign affairs minister, has been sharply critical of Ethiopian authorities throughout the two-year war.
The government has, in turn, accused him of trying to procure arms and diplomatic backing for rebel forces - charges he has denied.
In his sharpest comments on the war yet, Tedros told reporters in Geneva that food and healthcare were being used as weapons of war in Tigray, which is largely cut off from the outside world.
"There's no other situation globally in which 6 million people have been kept under siege for almost two years," Tedros said. "There is a very narrow window now to prevent genocide."
Ethiopian government spokesperson Legesse Tulu, Redwan Hussein, the national security advisor to the prime minister, and the prime minister's spokesperson Billene Seyoum did not immediately respond to requests for comment.
The Ethiopian government has repeatedly denied blocking humanitarian supplies to Tigray or targeting civilians. The conflict has killed thousands, displaced millions and left hundreds of thousands on the brink of famine.
Ethiopian forces and their allies have captured several towns in Tigray this week, raising fears that the advancing soldiers will commit abuses against civilians.
A joint investigation by the United Nations and Ethiopia's state-appointed human rights commission last year found that all sides fighting in the Tigray war committed violations that may amount to war crimes.
Ethiopia's government said this week that its forces respect human rights.
The Tigray conflict is rooted in long-running rivalries between regional power blocs over control of Ethiopia as a whole and in deep disagreements over how power should be balanced between federal and regional authorities.
Ethiopian authorities have previously accused Tedros of supporting Tigray forces, without providing evidence.
"Yes, I'm from Tigray, and yes, this affects me personally. I don't pretend it doesn't," Tedros said on Wednesday.
"I have many relatives in some of the most affected areas. But my job is to draw the world's attention to crises that threaten the health of people wherever they are."
(Reporting by Nairobi Newsroom; Editing by Alexandra Hudson)
