U.S. Embassy Urgent Warning of Possible Mass Casualty Attack in Moscow The U.S. Embassy in Moscow has issued an urgent security warning and announced that there is a "credible" threat of a possible mass casualty incident at the T Complex Museum on Saturday. This embassy has announced that US officials are coordinating with Russian officials in response to this threat. The American Embassy asked the citizens of the country to stay away from the museum and its surrounding areas, stay away from crowded places, stay alert and follow the news of the local media for new information.