The war in Iran has sparked chaos across financial markets, leaving some investors and market makers reluctant to take on risk, making trading harder and costlier - a scenario regulators watch closely. None of the world's biggest markets, from U.S. Treasuries, to gold, to currencies have ​been spared, investors and traders said. In Europe, hedge funds, which now dominate bond trading, added to those dynamics as they rapidly unwound a number of bets this month.[…]