Rare coordination between the United States and Japan to strengthen the yen may be weakened by a policy divide over how the Bank of Japan should respond. U.S. Treasury Secretary Yellen sees tighter monetary policy as important to tackling yen weakness, while Japanese Prime Minister Kishi Sanae is cautious about raising interest rates because of the potential hit to the economic recovery. The disagreement leaves the joint effort exposed to conflicting priorities even as the Bank of Japan's benchmark interest rate remains at 1%.