The number of Britons killed by the Asian tsunami is likely to double earlier estimates, British Foreign Secretary Jack Straw said Friday, calling efforts to identify thousands of deteriorating bodies one of the biggest forensic operations ever. Straw, visiting Thailand's tsunami-affected Phuket island, told a news conference that the number of Britons confirmed dead had risen to 49, while the number of missing _ listed "as very likely to have been involved as victims" _ had jumped to 391 from 159. The British government earlier estimated that 199 of its nationals died. Most of the British victims were in Thailand. The missing include people who were seen in the water or in damaged buildings, or who would have been expected to have checked in with friends or relatives but have not been heard from since the Dec. 26 disaster, Straw said. Thousands of foreign tourists were among those killed when massive quake-spawned waves struck beach resorts in southern Thailand, one of 11 countries hit. Officials say the overall death toll will exceed 150,000. Thailand so far has confirmed 5,291 deaths, and reported another 3,716 people missing.