WASHINGTON—U.S. stocks retreated Wednesday, erasing strong gains, after the Federal Reserve signaled an interest rate hike could be coming soon, while supply concerns stemming from tension between Russia and Ukraine saw oil prices touch highs not seen since 2014. Wall Street ended the day in mixed territory after spending most of the day up roughly 2 percent. Stocks shed those gains following an afternoon policy update from the Fed and press conference by Fed Chairman Jerome Powell, which suggested the Fed would push forward with interest rate hikes. The Dow Jones Industrial Average closed down 0.38 percent, while the S&P 500 fell 0.15 percent and the Nasdaq Composite gained just 0.02 percent. The MSCI world equity index, which tracks shares in 45 nations, was largely flat. In its latest policy update, the Fed signaled it is likely to raise U.S. interest rates in March and reaffirmed plans to end its …