More than 11,000 children are known to have been killed or maimed in Yemen's civil war since it escalated nearly eight years ago, the United Nations said Monday.

"The true toll of this conflict is likely to be far higher," said the children's agency UNICEF about the casualties of the world's worst humanitarian crisis.

"Thousands of children have lost their lives, hundreds of thousands more remain at risk of death from preventable disease or starvation," said UNICEF executive director Catherine Russell.

About 2.2 million Yemeni children are acutely malnourished, one quarter of them aged under five, and most are at extreme risk from cholera, measles and other vaccine-preventable diseases, UNICEF said.

Yemen's war broke out in 2014 and quickly saw Iran-backed Huthi rebels seize the capital Sanaa, prompting Saudi-led forces to intervene to prop up the government the following year.

Hundreds of thousands have died since, either as a result of fighting or indirectly through unsafe drinking water, disease outbreaks, hunger and other impacts.

The agency's latest numbers confirm 3,774 child deaths between March 2015 and September 2022.

A UN-brokered truce lasted for six months until October 2, but warring parties then failed to agree on an extension.

Since then at least 62 children have been killed or wounded, said UNICEF.

"The urgent renewal of the truce would be a positive first step that would allow critical humanitarian access," Russell said.

"Ultimately, only a sustained peace will allow families to rebuild their shattered lives and begin to plan for the future."

The UN agency also said 3,904 boys had been recruited into the fighting over the years, and that more than 90 girls had been given roles including working at checkpoints.

UNICEF appealed for $484.4 million in funding to tackle the humanitarian crisis.

"If the children of Yemen are to have any chance of a decent future... all those with influence must ensure they are protected and supported," said Russell.