"The intensification of airstrikes is alarming, and we once again remind all parties to the conflict to respect their obligations under international humanitarian law," it said.
What we know about the strike
The attack on midnight Friday targeted a camp for displaced people in the town of Dedebit in northwestern Tigray.
It came just hours after the Ethiopian government called for "national reconciliation," announcing amnesty for opposition leaders from several ethnic groups, and senior officials of the rebel Tigray People's Liberation Front (TPLF).
Reports of the airstrike could not be identified independently as access to Tigray is restricted, and the region remains under a communications blackout.
Humanitarian crisis unfolds in Ethiopia
'Mass civilian casualties'
The UN humanitarian agency reported last month that airstrikes on Tigray between December 19 and 24 caused "mass civilian casualties."
Earlier this month, the UN said three Eritrean refugees, including two children, had been killed in an airstrike Wednesday on a refugee camp in Tigray.
Ethiopia's Tigray, a mountainous region of 5 million people, has been ravaged by a war that broke out between Tigrayan forces and federal troops 14 months ago.
The war has threatened to tear apart Africa's second-most populous country.
Three Eritrean refugees, including two children, were killed in an airstrike on a camp in Tigray, according to the UN refugee agency.