LONDON: Months of 'brutal' conflict in Yemen have killed or injured more than 1,000 children, and the number of young people recruited or used as fighters has soared, the United Nations children's agency (Unicef) said on Wednesday.

Some 400 children have been killed and more than 600 injured, an average of eight casualties every day, since fighting escalated at the end of March, according to Unicef.

A Saudi-led Arab coalition has been bombarding the Iranian-allied Houthi rebel movement, Yemen's dominant force, since late March in a bid to reinstate exiled President Abd-Rabbu Mansour Hadi, who has fled to Riyadh.

The war has killed more than 4,300 people, many of them civilians, and spread disease and hunger throughout the country.

More than 1.3 million people have been forced to flee their homes since March, and nearly 10 million children, 80 per cent of the country's under-18 population, need urgent humanitarian aid, Unicef said in a report released on Wednesday.

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"Children are bearing the brunt of a brutal armed conflict which escalated in March this year and shows no sign of a resolution," the United Nations (UN) agency said.

"This conflict is a particular tragedy for Yemeni children... (they) are being killed by bombs or bullets and those that survive face the growing threat of disease and malnutrition," Unicef Yemen representative Julien Harneis said.

The report Yemen: Childhood Under Threat said the number of children recruited or used in the conflict had more than doubled to 377 so far in 2015 from 156 in 2014.

All warring sides in Yemen are increasingly using teenage boys, who see fighting as a way to support their families financially, to swell their ranks, Unicef said.

A quarter of Yemen's health facilities, around 900, have closed since March, while shortages of medicines and medical supplies have disrupted those that remain open, according to the UN body, which said the health system was "crumbling".

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More than 2.5 million children under the age of 15 are at risk of contracting measles, while nearly 2 million are likely to suffer from malnutrition this year, almost one million more than in 2014, Unicef said.

"I would sell everything I have to ensure my children's well-being... what really disturbs me is how difficult it has become to get proper medical treatment," Umm Faisal, mother of an 18-month-old baby in Yemen, told Unicef.