GENEVA, Dec 6 (Reuters) - The United Nations asked on Wednesday for $18 million to help hundreds of thousands of Somalis displaced by floods which have have submerged villages, cut off roads and drowned farmlands in the Horn of Africa. Eric Laroche, the U.N. resident and humanitarian coordinator for Somalia, said the worst floods in decades had added to the woes of one of Africa's poorest countries, where there is no effective central government, basic services or infrastructure. "The humanitarian crisis of the Somali people, exhausted by years of conflict and disaster, is now deepening," he said in a statement released in Geneva. U.N. officials have previously said insecurity in Somalia, where an interim government is pitted against rival Islamists in a conflict some fear will escalate to all-out war, threatened to hamper efforts to help those uprooted by the floods. Some 350,000 people in Somalia, mostly in southern and central areas of the country, have been seriously affected by the floods which followed a devastating drought last year. The United Nations said up to 900,000 might become affected in coming weeks if persistent rains continue. Its financial appeal is meant to help provide water and sanitation, food, education, health care and other assistance in the country. Another $10 million has already been funded through the U.N.'s Complex Emergency Response Fund.