What we know about US solider accused of spying for Russia

A spy scandal allegedly involving a U.S. soldier is causing national security concerns. A source tells ABC News the soldier is an Army Lieutenant Colonel, a senior officer rank, working on this British base that serves as the headquarters for NATO's Rapid Reaction Corps, accused of spying for Russia. He was an officer who's probably a major, had access to very sensitive military information. So how NATO would react if Russia... ...were to do something such as invade a NATO country. And we already know that's already a major concern. So he would have access to this. That NATO unit coordinates large-scale training exercises and orchestrates NATO ground forces in a crisis. This certainly is very concerning. He would have received non-stop counterintelligence briefings because we know that Russia would want to penetrate this unit. And if he did, then this is a serious, significant... I can't. Action by the FBI and our counterparts in the UK. The 41-year-old soldier who has not been identified is being held in London, facing charges from British authorities and the U.S. Army. Brigadier General Sean Stinson, who oversees the Army's counterintelligence command, warning, quote, the alleged conduct of a senior soldier entrusted with sensitive information is a sobering reminder that insider threats are real and persistent. Russian President Vladimir Putin's press secretary is pushing back against the allegation, saying, quote, the soldier has nothing to do with us. Reena Roy, ABC News, New York.