Russian President Vladimir Putin cautioned the West on Friday against arming Syrian rebel forces, which he said included "terrorist" groups, and warned that a swift exit by President Bashar al-Assad risked creating a dangerous power vacuum. "If the United States ... recognizes one of the key Syrian opposition organizations, al-Nusra, as terrorist ... how can one deliver arms to those opposition members?" Putin told a panel with German Chancellor Angela Merkel. "Where will they end up? What role will they play?"