The United Nations appealed for nearly $460 million Wednesday to provide immediate help to millions of victims of the worst floods in Pakistan in living memory and said it will need millions more to help rebuild the devastated country."Make no mistake, this is a major catastrophe," UN humanitarian chief John Holmes told diplomats from several dozen countries in launching the appeal. "The affected population is estimated to be more than 14 million — almost one-tenth of Pakistan's population."The U.N. Office for the Coordination of Humanitarian Affairs, which Holmes heads, said at least six or seven million flood victims require immediate humanitarian assistance including shelter, food, clean water, sanitation and medical care.Before the $459.7 million appeal was launched, the UN already had pledges and commitments of more than $150 million but over $300 million is still needed, Holmes said.He told reporters after Wednesday's pledging conference that he was encouraged by the turnout and generosity of donors, and the commitment of many countries to continue helping Pakistan.The United States made the biggest pledge, $71 million. Britain said it has given 5 million pounds to the U.N. children's agency, UNICEF, for water and sanitation; 5 million pounds to the Pakistani Emergency Response Fund; 10 million pounds to rebuild bridges and 750,000 pounds for emergency seed money as well as 2,500 tents, and 4,500 pounds for Pakistan's emergency radio broadcast program. Other donations included $10 million from Australia and $5 million from Kuwait."More than one week after the initial arrival of the floods, huge areas of the country remain without power, clear water or communications," Holmes said.Among the big ticket items needed is $150.5 million to buy food and $110.5 million to provide clean water for 6 million people, he said. Another $105 million is needed to provide tents or plastic sheeting for 2 million people, he said, and $56.2 million for emergency health care.According to the UN, over 1,200 people have died and at least 288,000 homes have been damaged or destroyed in the flooding.Pakistan's UN Ambassador Abdullah Haroon called the floods a particularly "savage attack by nature" and praised the United Nations for "assisting in every way possible."Haroon said the number of people affected could rise further because the floods are spreading and a week of further rains is predicted."We might have it even up to 16 million," he said.Noting that the Asian tsunami in 2004 displaced less than 2 million people, Haroon said, "This is seven times the amount. This is horrendous."Holmes said the appeal will cover the immediate relief period of up to 90 days and will be revised in 30 days to take account of the impact of continued flooding.