U.S. stock benchmarks on Monday declined ahead of the start of the final gathering of the U.S. Federal Reserve in 2021 and as investors continued to wrestle with concerns about omicron, as the variant spread in parts of Europe, causing full and partial lockdowns. The Dow Jones Industrials Average DJIA, -0.89% fell nearly 320 points, or 0.9%, to 35,651. The S&P 500 index SPX, -0.91% also closed down 0.9% to reach 4,668, falling below 4,700. Both benchmarks registered their worst daily declines since Dec. 1, FactSet data show. The Nasdaq Composite Index COMP, -1.39% ended down 1.4% to reach 15,413. The Fed concludes a meeting of its rate-setting committee on Wednesday. The Federal Open Market Committee, headed by Chairman Jerome Powell, is expected to move more quickly to wind down its bond-buying program and signal that it will raise interest rates next year to curb inflation. Consumer data published Friday showed consumer prices increased last month at the fastest annual rate since 1982, which is likely to embolden the Fed, with the rate of inflation well above its target 2% annual rate. Meanwhile, U.K. Prime Minister Boris Johnson warned of a tidal wave of omicron cases, re-igniting jitters about the global economic impact of the COVID pandemic in 2022 and beyond.