The Houthi rebels have not taken any action to protect children in Yemen during the country's four-year war, a UN envoy said on Monday. “They have continued to recruit children, along with shelling hospitals and schools,” said Virginia Gamba, the UN Secretary General's representative for children and armed conflict. The Arab Coalition and UN signed a plan on Monday to reinforce the protection of children affected by the conflict in Yemen. Children in Yemen are victims of what the UN calls the world’s worst humanitarian crisis as poverty and disease have brought the country to its knees. Yemen has the highest level of child labour in the Arab world, the International Labour Organisation says. Ms Gamba said she was certain Saudi Arabia would play a crucial role in the protection of children. “After years of destructive conflict, the children of Yemen continue to suffer unimaginable violence," she said. "Today’s signature is an important addition to the measures already in place to enhance the protection of boys and girls in Yemen." Ms Gamba said the agreement presented a clear commitment by the Coalition that would result in action to improve the protection of children in Yemen. The agreement, signed in Saudi Arabia, will focus on preventive action and provision of services for child survivors. “I’m hoping that this will become a model to contain this issue in the world,” Ms Gamba said. She reminded all parties of their obligation to protect civilians, of whom children are the most vulnerable, and called for a focus on ensuring peace in Yemen. Ms Gambo said her office submitted a report to UN Secretary General Antonio Guterres every three months. “We are not silent about the tragedies that are happening to children in Yemen,” she said. Three quarters of Yemen's population of 29 million are in need of humanitarian aid, with more than 10 million on the brink of starvation, the UN said. The Houthis' refusal to implement the terms of a UN-brokered ceasefire in Hodeidah has dashed hopes of an early political settlement to Yemen's conflict, with rebel shelling reported in the city's east on Monday. The clashes were the heaviest since the ceasefire went into effect on December 18 after UN-led peace talks in Sweden. "The Houthis are escalating their military operations after targeting army positions in eastern Hodeidah," Fayad Nouman, undersecretary of the Ministry of Information, told <em>The National.</em> The rebel’s attacks are a clear breach of the Stockholm agreement, Mr Nouman said. The Houthis are seeking to cut off the main route from the eastern part of Hodeidah to Khokha and Mokha further south on the Red Sea coast, Col Waddah Aldbish, spokesman for the Arab Coalition, told <em>The National</em>. Rebel shelling on Sunday killed two men and a child, 8, at a gathering near a public market in the centre of Hays district in southern Hodeidah. Another person was severely injured. The ceasefire has broadly held despite sporadic clashes but the UN is struggling to implement a troop withdrawal, a confidence-building measure meant to clear the way for a broader peace settlement.