Famine is now knocking on the door of Ethiopia's Tigray region, where a civil war that erupted last year has drastically cut the food supply and prevented relief workers from helping the hungry, the top humanitarian official at the United Nations has warned.

In a confidential note to the U.N. Security Council, Mark Lowcock, the undersecretary general for humanitarian affairs, said sections of Tigray, a region of more than 5 million people, are now one step from famine — in part because the government has obstructed aid shipments.

The note, seen by the New York Times, was submitted Tuesday under a Security Council resolution requiring such notification when conflicts cause famine and widespread food insecurity.

"These circumstances now arise in the Tigray region of Northern Ethiopia," Lowcock said in the note. While below-average rain, locusts and the COVID-19 pandemic have all contributed to food scarcity, he said, "the scale of the food crisis Tigray faces today is a clear result of the conflict and the behavior of the parties."

Ethiopia, Africa's most populous country after Nigeria, has been convulsed by the Tigray conflict since last November. Prime Minister Abiy Ahmed and neighboring Eritrea ordered their military forces into the region to crush Abiy's political rivals and strengthen his control.

What Abiy, a Nobel Peace Prize laureate, predicted would be a short operation has instead become a quagmire that threatens to destabilize the Horn of Africa. Ethiopian and Eritrean troops have been accused of ethnic cleansing, massacres and others atrocities in Tigray that amount to war crimes.

Lowcock urged Security Council members "to take any steps possible to prevent a famine from occurring."

His warning was echoed by former U.S. ambassador to the United Nations Samantha Power, the administrator of the United States Agency for International Development, the main U.S. government provider of humanitarian assistance to needy countries.

"The risk of famine in Ethiopia looms for the first time in over 30 years," Power said. "Eritrean troops must leave Tigray, the Ethiopian government must grant unimpeded humanitarian access and punish human rights abusers, and a political solution must be reached."