NEW YORK, Feb 17 : Oil prices fell about 2 per cent to a two-week low on Tuesday on hopes tensions between the United States and Iran were easing after Iran's foreign minister said the countries had reached an understanding on the main "guiding principles" of their nuclear talks. Brent futures fell $1.41, or 2.1 per cent, to $67.24 a barrel at 11:50 a.m. EST (1650 GMT), while U.S. West Texas Intermediate (WTI) crude fell 65 cents, or 1.0 per cent, to $62.24 in volatile trading, putting both