WASHINGTON, Oct 7 (Reuters) - The U.S. government this week bought $290 million in supplies of a drug designed to treat blood cell injuries following radiological and nuclear emergencies as part of what it said were long-standing efforts to prepare for potential health impacts from threats to national security.When asked whether the purchase, announced Tuesday, was linked to tensions with Russia following its invasion of Ukraine, an HHS spokesperson said it was part of ongoing efforts to prepare for a wide range of threats including chemical, biological, radiological, nuclear, and emerging infectious diseases.Register now for FREE unlimited access to Reuters.comWith funds from the Project Bioshield Act, a law passed in 2004, HHS supports development of diagnostics, vaccines and treatments to respond to potential health impacts of such threats.Concerns about potential use of nuclear weapons have risen after Russian President Vladimir Putin has issued warnings in recent weeks that he is ready to use them to defend Russia, cautioning it was no bluff.read moreRadiation sickness occurs when a person's entire body is exposed to a high dose of penetrating radiation, reaching internal organs in a matter of seconds."