"Putin Vows to Uncover Mastermind Behind Lethal Concert Shooting"

Russian President Vladimir Putin has vowed to uncover the masterminds behind the deadly attack on a concert hall near Moscow that claimed the lives of at least 144 people. While Islamic State has claimed responsibility for the attack, U.S. officials believe it was carried out by the group's Afghan branch, ISIS-K. Russia alleges links to Ukraine, a claim denied by Kyiv and rejected by the United States.