BANGKOK - Thailand, Laos, Cambodia and Vietnam failed on Tuesday to agree on whether Laos should proceed with a controversial $3.5 billion Mekong River dam project, a decision they said should be handled at ministerial level.The four lower Mekong countries were unable to find a common conclusion a meeting in the Lao capital Vientiane. There was "still a difference in views" between them over the project, the Mekong River Commission, of which the four countries are members, said in a statement.