US President Barack Obama Saturday signed into law tough new sanctions targeting Iran's central bank and financial sector, in a move that could intensify a brewing Gulf showdown. The measures, meant to punish Iran for its nuclear program, were contained in a mammoth $662 billion defense bill, which Obama signed despite having reservations that it ties his hands on setting foreign policy. The sanctions are meant to hit Iran's crucial oil sector and require foreign firms to make a choice between doing business with Tehran's financial sector and central bank or the mighty US economy and financial sector. Foreign central...