(Reuters) - The S&P 500 and the Nasdaq retreated on Tuesday as Federal Reserve Chair Jerome Powell warned the U.S. economic recovery remained far from complete, with a selloff in some of the biggest technology companies also weighing on sentiment. The domestic rebound could still slip into a downward spiral if the coronavirus is not effectively controlled and growth sustained, Powell said, in a call for more help to businesses and households. “Markets are worried about what the Fed knows that we don’t know,” said John Augustine, chief investment officer at Huntington National Bank in Columbus, Ohio. “The things that are obvious to us are that small businesses are closing and unemployment remains high in the services sector. The Fed aggressively wants to address both of those with more fiscal stimulus.” Comments from officials that a stimulus deal was still possible had lifted the three main stock indexes on Monday, helping them recoup losses from last week that were sparked by news that President Donald Trump had contracted COVID-19. Trump returned to the White House on Monday from the Walter Reed Medical Center military hospital, but faced fresh backlash for removing his mask upon his return and urging Americans not to fear the disease that has killed more than 209,000 in the United States. House Speaker Nancy Pelosi and Treasury Secretary Steven Mnuchin spoke by phone on Monday about fresh relief measures and were preparing to talk again on Tuesday. Seven of the 11 major S&P sectors were up, with gains led by the battered energy sector. A rotation into value-linked sectors such as industrials also boosted the blue-chip Dow, but the Nasdaq slipped further away from record highs following a dip in shares of heavyweight technology mega-caps. Amazon.com Inc, Apple Inc, Facebook Inc and Google-owner Alphabet Inc fell between 0.8% and 2.2% as reports said a U.S. House of Representatives’ antitrust report contains a “thinly veiled call to break up” the companies. At 11:29 a.m. ET, the Dow Jones Industrial Average was up 35.20 points, or 0.13%, at 28,183.84, the S&P 500 was down 5.19 points, or 0.15%, at 3,403.44, and the Nasdaq Composite was down 62.46 points, or 0.55%, at 11,270.03. Boeing Co fell 2.8% after the planemaker cut its rolling 20-year forecast for airplane demand due to the fallout from the COVID-19 pandemic. U.S.-listed shares of BioNTech BNTX.O jumped 6.3% after the European health regulator said it had started a real-time review of the COVID-19 vaccine being developed by the German biotech firm and U.S. drugmaker Pfizer Inc. Pfizer"s shares dipped 0.1%. Shares of audio device makers Sonos Inc and Logitech fell 5.2% and 4.7%, respectively, after their speakers were removed from Apple’s online stores. Advancing issues outnumbered decliners by a 2.18-to-1 ratio on the NYSE and by a 1.96-to-1 ratio on the Nasdaq. The S&P index recorded 24 new 52-week highs and no new low, while the Nasdaq recorded 93 new highs and seven new lows.