The United States backed up Tuesday its long-held position on the need to preserve samples of smallpox, saying keeping a stockpile of the virus counters the threat of germ warfare. \"We are concerned that the smallpox virus still exists outside the official laboratories and could be released intentionally or used as a virus weapon,\" US Health and Human Services Secretary Kathleen Sebelius told the World Health Organisation\'s 64th assembly. \"The WHO on review on the smallpox research programme concluded definitely that additional research is needed to protect public health if this occurred,\" she added. Currently only the United States and Russia maintain the last strains of the virus which was eradicated in the 1980s. For over two decades the WHO\'s 193 member states have been at a deadlock on the need to preserve the samples. The WHO, the public health arm of the United Nations, has studied a proposal seeking to extend by another five years the use of smallpox samples for research, Sebelius said. \"But let me be clear, we are committed to the eventual destruction of the virus stocks,\" she added.