GENEVA (Reuters) - The United States called on Wednesday for closer international cooperation to prevent terrorist groups from developing or using biological weapons, a threat it said was growing. Secretary of State Hillary Clinton said countries must strengthen their ability to detect and respond to suspicious outbreaks of infectious disease that could be caused by pathogens falling into the wrong hands. "Unfortunately the ability of terrorists and other non-state actors to develop and use these weapons is growing. Therefore this must be a renewed focus of our efforts," she said in a speech in Geneva. "Because there are warning signs and they are too serious to ignore."