More than 400,000 people have "crossed the threshold into famine" in Ethiopia's war-torn Tigray region, a senior UN official said, appealing for urgent humanitarian action to help the millions affected by the brutal eight-month long conflict.

Fighting between the Ethiopian government and the Tigray People's Liberation Front (TPLF) was reignited last month when the rebels launched a major counter-offensive that saw them retake their regional capital of Mekele.

This week two key bridges allowing desperately-needed aid into the region were destroyed, prompting fears the federal government was seeking to choke off humanitarian assistance -- a charge Addis Ababa denied.

Yesterday saw the UN Security Council hold its first public meeting on a conflict that has left thousands of dead and plunged hundreds of thousands into hunger.

Ramesh Rajasingham, Acting Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator, told that meeting that the situation had "worsened dramatically" as the conflict had reignited in recent weeks.

"More than 400,000 people are estimated to have crossed the threshold into famine and another 1.8 million people are on the brink of famine," he said.

"Some are suggesting that the numbers are even higher. 33,000 children are severely malnourished."

"The lives of many of these people (in Tigray) depend on our ability to reach them with food, medicine, nutrition supplies and other humanitarian assistance," he added.

"We need to reach them now. Not next week. Now."

Ethiopia has rejected charges that it planned to choke off aid to the region.

"The insinuation that we are planning to suffocate the Tigrayan people by denying humanitarian access and using hunger as a weapon of war is beyond the pale," Deputy Prime Minister Demeke Mekonnen told diplomats gathered at a hotel in the capital Addis Ababa.

Officials are "using every ounce of our strength to extricate" Tigrayan civilians "from the dire situation they find themselves in", he added.

Wounded captive Ethiopian soldiers arrive at the Mekele Rehabilitation Centre in Tigray

Prime Minister Abiy Ahmed, winner of the 2019 Nobel Peace Prize, sent troops into Tigray last November to detain and disarm leaders of the regional ruling party, the Tigray People's Liberation Front (TPLF).

He said the move was in response to TPLF attacks on federal army camps, and declared victory within weeks after federal forces took the regional capital Mekele.

But after the rebels, having rebranded themselves the Tigray Defence Forces (TDF), retook Mekele and asserted control over most of the region, the government announced a unilateral ceasefire that the TDF has dismissed as "a joke".

Senior UN official Rosemary DiCarlo urged the group to "immediately and completely" endorse the ceasefire.

"A ceasefire observed by all parties would not only facilitate the provision of humanitarian aid but would also be a starting point for the necessary political efforts to chart a way out of the crisis," Ms DiCarlo said.