A senior US official said Wednesday that a proposed treaty banning cluster bombs would hurt world security and endanger US military cooperation on humanitarian work with countries that sign the accord. Stephen Mull, an assistant secretary of state, briefed reporters at the State Department to explain why the United States was not attending a gathering in Ireland of representatives of more than 100 nations working on a treaty to ban the bombs blamed for killing or maiming civilians as their mini-bombs explode months or years after they are dropped. A critic of the US position, Marc Garlasco, senior military analyst for Human Rights Watch, said in a telephone interview from Dublin that it was outrageous for Mull to link US military humanitarian work with the United States' "failed policy on cluster munitions." That would hinder humanitarian work of the type the United States is involved in now in Myanmar and China, he said. American warships and planes often are used to respond to earthquakes, typhoons, cyclones and other disasters around the world.