* Stocks fall after initial gains as risks bubble up * Oil prices fall as profit-taking tames OPEC+ surge * U.S. Treasury yields fall; Have yields already peaked? (Updates with U.S. markets midday trading, comment) NEW YORK, July 6 (Reuters) - Global stock prices fell sharply Tuesday - after some indexes briefly touched new highs - as tumbling bond yields, lower crude prices, China’s latest tech crackdown and expectations of a hawkish Fed report on Wednesday waved red flags at investors. With risks percolating, “it seems like the winning streak has snapped,” said Edward Moya, senior market analyst for the Americas at OANDA. Around 1840 GMT, the Dow Jones Industrial Average was down 252.69 points, or 0.73 percent, to 34,533.66. The broad S&P 500 index was off 16.98 points, or 0.39 percent, at 4,335.36. The tech-heavy Nasdaq Composite slipped 1.87 points, or 0.01 percent, to 14,637.46. Bond yields also were lower as concerns about a revving global economy eased. The yield on 10-year U.S. Treasury notes was down 6.5 basis points to 1.367%. A month ago, yields were widely expected to rise in the second half, possibly reaching 2% by year-end. Now, the consensus thinks yields may have peaked for the year. Oil pulled back on Tuesday from its recent rally after OPEC+ producers canceled a meeting due to clashes over plans to increase supply to meet rising global demand. The crude spike was based largely on posturing, since suppliers are still going to increase output, Moya said. “Demand is just too strong,” he added. Investors will watch for minutes from the U.S. Federal Reserve’s Federal Open Market Committee (FOMC), due Wednesday. The market expects them to confirm a hawkish - or anti-inflation - tilt, and a benign readout could trigger a rally. The Organization of the Petroleum Exporting Countries (OPEC) and allies, known as OPEC+, abandoned talks Monday after the United Arab Emirates rejected an eight-month extension to output curbs. Some OPEC+ sources said a new meeting would take place in coming days and would lead to a boost in August. Crude prices earlier reached $77.66 - the highest level since October 2018 - and U.S. crude hit its highest since late 2014 at $76.90 a barrel. Oil is up about 50% this year and over 385% since last year’s COVID-driven slump. TECH TROUBLES Chinese ride-hailing company Didi Global Inc shares slumped more than 20% after Chinese regulators ordered the company’s app taken down days after its $4.4 billion listing on the New York Stock Exchange. Other U.S.-listed Chinese e-commerce firms, including Alibaba Group, Baidu Inc and JD.com, fell 3.5% to 4.6%. Hong Kong marked its sixth day of losses and China’s CSI300 dipped to an almost two-month-low, after the Cyberspace Administration of China ordered an investigation into Didi. China will step up supervision of Chinese firms listed offshore, and improve regulation of cross-border data flow and security, Xinhua quoted the cabinet as saying. Additional reporting by Marc Jones in London, Scott Murdoch in Singapore; Editing by Alison Williams, John Stonestreet, Alexander Smith and Cynthia Osterman Our Standards: The Thomson Reuters Trust Principles.