** S&P 500 energy index .SPNY falls ~2% as oil prices ease

** Brent crude LCOc1 futures down 1.4% at $67.71/barrel; U.S. West Texas Intermediate $(WTI)$ crude futures CLc1 fall 0.2% to $62.79/barrel

** Prices fall after Iran's foreign minister said the United States and Iran reached an understanding on the main "guiding principles" of their nuclear talks, easing investor concerns about tensions escalating O/R

** Oil majors Exxon Mobil XOM.N and Chevron CVX.N down 1.5% and 1.2%, respectively

** APA Corp APA.O, Diamondback Energy FANG.O, Expand Energy EXE.O and EQT Corp EQT.N among biggest percentage losers on the energy index, slip between 2.5% and 3.1%

** Refiners Marathon Petroleum MPC.N and Valero Energy VLO.N dip 1.6% and ~1%, respectively

** Oilfield services companies: SLB SLB.N down 1.3%, Baker Hughes BKR.O falls ~2% and Halliburton HAL.N dips 1.2%

(Reporting by Dharna Bafna in Bengaluru)

((Dharna.bafna@thomsonreuters.com))