ISTANBUL - President Tayyip Erdogan on Monday said Turkey could cut off the pipeline that carries oil from northern Iraq to the outside world, piling more pressure on the semi-autonomous region over its independence referendum."After this, let's see through which channels the northern Iraqi regional government will send its oil, or where it will sell it," Erdogan said in a speech at a forum in Istanbul."We have the tap. The moment we close the tap, then it's done."He stopped short of saying that Turkey had decided to close off the oil flow. Hundreds of thousands of barrels of oil a day flow through the pipeline in Turkey from the northern Iraq region.