The UN World Food Program on Friday appealed for safe access to the Yemeni city of Taiz, saying that fighting between warring factions had blocked food supplies and left thousands of people in extreme hunger.
The last UN food aid to reach Taiz, Yemen's third city, was more than five weeks ago when food was distributed to nearly 240,000 people, it said.
"We plead for safe and immediate access to the city of Taiz to prevent a humanitarian tragedy as supplies dwindle, threatening the lives of thousands - including women, children and the elderly," WFP regional director Muhannad Hadi said in a statement.
"These people have already suffered extreme hunger, and if this situation continues the damage from hunger will be irreversible."
On Wednesday, warplanes from the Saudi-led coalition that backs Yemen's government bombed the Iran-allied Houthi movement across Yemen and dropped weapons to Islamist militias in Taiz, situated in the southwest.
Ten of Yemen's 22 governorates were assessed as being in an emergency food situation in June, one step below famine on a five-point scale. The assessment has not been updated since then, partly because experts have not managed to get sufficient access to survey the situation.
About a third of the country's population, or 7.6 million people urgently require food aid, the WFP said.