Platinum futures climbed above $1,870 an ounce to an 11-week high as a weaker U.S. dollar and renewed precious-metals demand supported the market. The dollar index hovered near 98.8 on Friday and was on track for a nearly 1 percent weekly loss as investors questioned whether the Treasury's expanded purchases of longer-dated U.S. debt could stabilize the economy or provide lasting relief from elevated borrowing costs. Lower Treasury yields earlier in the week, expectations that the Federal Reserve could leave interest rates unchanged in September and persistent global platinum supply deficits with low inventories further supported non-yielding assets. Higher oil prices linked to the United States preparing sweeping new economic sanctions against Iran, along with broader Middle East tensions, added inflation and economic uncertainty and encouraged demand for precious metals as a hedge.