The head of the United Nations warned Monday of a "death sentence" against war-torn Yemen after a donor conference yielded less than half the funds needed to prevent a devastating famine.

The UN had appealed for $3.85 billion to pay for urgently needed aid, but just $1.7 billion was offered at a virtual pledging conference.

"Millions of Yemeni children, women and men desperately need aid to live. Cutting aid is a death sentence," UN Secretary-General Antonio Guterres said.

Describing the outcome as "disappointing", he said the pledges were less than the UN received in 2020, when donations were first hit by the coronavirus downturn, and a billion dollars shy of funds offered in the 2019 appeal.

"The best that can be said about today is that it represents a down payment. I thank those who did pledge generously, and I ask others to consider again what they can do to help stave off the worst famine the world has seen in decades," Guterres said in a statement.

Tens of thousands of people have been killed and millions pushed to the brink of famine in the six-year-old Yemen conflict, which the UN describes as the world's worst humanitarian crisis
Tens of thousands of people have been killed and millions pushed to the brink of famine in the six-year-old Yemen conflict, which the UN describes as the world's worst humanitarian crisis AFP / ESSA AHMED

More than 100 governments and donors took part in the conference, co-hosted by Sweden and Switzerland, as Yemen's Huthi rebels push to seize the government's last northern stronghold.

The six-year-old civil war pits the Iran-backed insurgents against an internationally recognised government backed by a Saudi-led military coalition.

Guterres said the only way of relieving the suffering of Yemeni people was to secure a nationwide ceasefire and a political solution to end a grinding conflict that has plunged the nation into the world's worst humanitarian crisis.

"There is no other solution," the UN chief said. "The United Nations will continue to stand in solidarity with the starving people of Yemen."

A Yemeni girl sits at the Jaw al-Naseem camp for internally displaced people on the outskirts of the northern city of Marib on February 18, 2021. According to the latest UN data, more than 16 million Yemenis will face hunger this year
A Yemeni girl sits at the Jaw al-Naseem camp for internally displaced people on the outskirts of the northern city of Marib on February 18, 2021. According to the latest UN data, more than 16 million Yemenis will face hunger this year AFP / Nabil ALAWZARI

Some of the headline pledges on Monday, including $191 million from the United States and Saudi Arabia's $430 million, were smaller than last year's donations. However, Germany offered 200 million euros ($241 million), compared to $138 million last year.

Shrinking humanitarian budgets last year forced the closure of many programmes including health services and food distribution, heaping hardship on a country where some two-thirds of the population relies on some form of aid to survive.

According to the latest UN data, more than 16 million Yemenis, about half the 29-million population, will face hunger this year.

Nearly 50,000 are already starving to death in famine-like conditions.

The world body has warned that 400,000 Yemeni children under the age of five could die from acute malnutrition.

Displaced Yemenis receive food aid donated by a Kuwaiti charity in the western province of Hodeida on February 22, 2021. With aid funding dropping in 2020 amid the coronavirus downturn, the situation in the country has become even more dire
Displaced Yemenis receive food aid donated by a Kuwaiti charity in the western province of Hodeida on February 22, 2021. With aid funding dropping in 2020 amid the coronavirus downturn, the situation in the country has become even more dire AFP / Khaled ZIAD

"The money that we received today is not enough to stop the famine and we will need more," said Mark Lowcock, the UN's undersecretary general for humanitarian affairs.

Humanitarian groups including Save the Children also responded with frustration, saying the world was turning its back on Yemen.

"This means continued massive cuts to emergency food, water, shelter and medical support. The shortfall in humanitarian aid will be measured in lives lost," said Jan Egeland, Secretary General of the Norwegian Refugee Council, who is currently in Yemen.

"I told governments at the conference that I have just seen children who are already dying of starvation in Yemen," he said in a statement.

"It is in their power to prevent full-scale famine, or forever have this stain on their consciences. So far, they have failed to act."

Huthi spokesman Mohammed Abdul Salam also hit out at the pledges, saying they were an attempt by countries involved in the conflict to whitewash themselves.

"The conference... does not help Yemen as much as it helps the aggressor nations by giving them the opportunity to cleanse their record," he tweeted.

The conference comes as the US pushes to revive peace efforts.

President Joe Biden's administration has halted support to the Saudi-led military coalition, and reversed a terror blacklisting of the Huthis imposed last month by Donald Trump's outgoing administration -- a designation many warned could severely impede aid efforts.

But Huthi fighters have intensified operations against Saudi Arabia as coalition air strikes pound rebel positions in northern Yemen, as the insurgents push to seize the government's last northern stronghold of Marib.

US Secretary of State Antony Blinken on Monday urged the rebels to halt that battle and come to the negotiating table.

"The necessary first step is to stop their offensive against Marib, a city where a million internally displaced people live, and to join the Saudis and the government in Yemen in making constructive moves towards peace," he told the conference.

"The time is now to make this push to bring about a more stable, prosperous Yemen whose citizens will be able to rebuild their lives and at long last have hope for a better future."