An online video and messages purportedly claiming responsibility for a fire that analysts say damaged a centrifuge assembly plant at Iran’s underground Natanz nuclear site deepened the mystery Friday around the incident. The multiple, different claims by a self-described group called the “Cheetahs of the Homeland” included language used by several exiled Iranian opposition organizations, as well as focused almost entirely on Iran’s nuclear program, viewed by Israel as a danger to its very existence. The disparate messages, as well as the fact Iran experts had never heard of the group before, raised questions about whether Natanz again had faced sabotage by a foreign nation as it had during the Stuxnet computer virus outbreak believed to have been engineered by the U.S. and Israel.