TOKYO (Reuters) -Oil prices fell by about $2 on Thursday on expectations of a potential U.S.-Iran nuclear deal that could result in sanctions easing, while a surprise build in U.S. crude oil inventories last week heightened investor concerns about oversupply. U.S. West Texas Intermediate (WTI) crude futures slid $2.10, or 3.3%, to $61.05. Iran is willing to agree to a deal with the U.S. in exchange for the lifting of economic sanctions, an Iranian official told NBC News in an interview published on Wednesday.