The UN aid coordinator in Yemen announced Wednesday he was leaving his post just days after the UN envoy for the war-torn country also said he was stepping down.

"This is my last day here in Sanaa," McGoldrick told reporters in the Yemeni capital.

"I leave Yemen with a great deal of mixed emotion... sadness because of the suffering that is taking place, frustration because we haven't been able to do more for the people in this country."

"And at the same time, more and more people have become vulnerable because of this crisis".

The United Nations has not announced the appointment of a new aid coordinator for Yemen, which it says is facing the world's worst humanitarian crisis.

On Monday, the international body said UN Yemen envoy Ismail Ould Cheikh Ahmed would be stepping down in February, after nearly three years as the top negotiator for the country.

More than 9,200 people have been killed and millions displaced since Saudi Arabia and its allies joined the Yemeni government's war against rebels in 2015.

Another nearly 2,200 Yemenis have died of cholera amid deteriorating hygiene and sanitation conditions, the World Health Organisation says.

The United Nations last week made a record appeal for nearly $3 billion to combat imminent famine as well as cholera and diphtheria outbreaks in 2018.

Multiple rounds of UN-brokered peace talks between the Iran-backed Huthi rebels and the Saudi-supported government have failed to stem the fighting.