"There's no other situation globally in which 6 million people have been kept under siege for almost two years," the WHO director said 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.
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.
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.
Ethiopian forces and their allies, including Eritrea, have captured several towns in Tigray this week, raising fears that the advancing soldiers will commit abuses against civilians.
In return, Ethiopia's government said this week that its forces respect human rights.
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.
Addis Ababa has accused Tedros of supporting Tigray forces, without providing evidence, to which he has responded "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."