UN humanitarian officials on Friday voiced alarm over the 'dire' condition of civilians displaced by two months of warfare in northern Yemen and appealed for money to pay for aid. Military officials, meanwhile, said Zaidi Shiite rebels had launched a raid on a city in northern Yemen, triggering fierce clashes with the army that claimed 'huge casualties' on both sides. UN humanitarian chief John Holmes called for greater access to people who have fled their homes and urged donors to respond quickly to an emergency plea for 23.5 million dollars in aid. 'Tens of thousands of people have been displaced by the latest wave of fighting in northern Yemen alone, and the number is growing daily,' Holmes said at the start of a three-day visit to Yemen. 'I am here to see the situation for myself and galvanise support for the men, women and children whose lives have been overturned by this conflict,' he said. The United Nations says some 150,000 people have been displaced in northern Yemen in the past five years, including 55,000 since August 11 when fighting resumed between Shiite rebels and the military. Holmes, who visited Haradh in the northwestern province of Hajjah on Friday to inspect one of five camps sheltering displaced, said 'agencies are working hard to provide assistance where they can.' But, he added, 'they need better access and the support of the international community if they are going to overcome the challenges that they face on the ground.' He lamented that the UN has only received 3.8 million dollars since September 2 in response to a call for emergency funds of 23.5 million dollars to help Yemen's displaced. 'The money is simply not coming in fast enough to meet the requirements. I urge donors to come forward with increased contributions,' said the UN aid supremo. Andrej Mahecic, a spokesman in Geneva for the office of the UN High Commissioner for Refugees (UNHCR), warned: 'The civilian population continues to bear the brunt of the ongoing conflict and the humanitarian situation is dire.' A growing number of people in Saada governorate are fleeing into neighbouring provinces, often undertaking a five-day trek on foot, he told journalists. UN humanitarian agencies are providing aid to 75,000 people in northern Yemen, according to Elizabeth Byrs, a spokeswoman for the UN Office for the Coordination of Humanitarian Affairs (OCHA). But an operation to ferry in aid by road from neighbouring Saudi Arabia has been delayed for the past several days because of security concerns, a UNHCR official said in Riyadh. On the battlefront, Zaidi rebels launched an attack overnight on Saada, 240 kilometres (150 miles) north of Sanaa, in a bid to 'take control of the Palace of the Republic,' a symbol of state authority, a military source said on Friday. Heavy fighting ensued for nearly four hours with the army eventually repelling the attackers from different sides of the city and forcing them to retreat, according to another military source. The battle resulted in 'huge casualties on both sides,' the source said without elaborating. Fighting has been raging since August 11 between the army and the rebels, whom authorities accuse of being supported by groups in Iran and aiming to restore a Zaidi imamate. The rebels deny both claims and allege that Saudi Arabia is helping the Yemeni military. The government, which launched its offensive two months ago, twice announced ceasefires in September but they lasted only a few hours. The two sides accuse each other of not allowing the opening of humanitarian corridors. The media has been restricted access to the warzone, where the death toll from the offensive is believed to run into the hundreds. 