President Vladimir Putin warned on Thursday that Russian gas supplies to Europe could be disrupted if Moscow cuts the flow to Ukraine over unpaid bills, drawing a U.S. accusation that it is using energy "as a tool of coercion". In a letter to the leaders of 18 European countries, Putin made clear that his patience would run out over Kiev's $2.2 billion (1.3 billion pounds) gas debt to Russia unless a solution could be brokered urgently. Russia has nearly doubled the gas price it charges Ukraine, whose economy is in crisis, since pro-Moscow President Viktor Yanukovich was overthrown two months ago. Russia then ... (full story)