Stocks slumped, bonds sold off and the U.S. dollar continued to lose ground on Monday as President Trump’s new attacks on the chair of the Federal Reserve jolted investors.

The sell-off in U.S. stock markets, which reopened Monday after the Good Friday holiday, gained steam after Mr. Trump again targeted Jerome H. Powell, the Fed chair, in a social media post, calling him “a major loser” and urging a cut in interest rates.

The S&P 500 fell more than 3 percent, as did the technology-heavy Nasdaq Composite index. All of the major sectors in the S&P 500 were down, with the technology, energy and consumer discretionary sectors hardest hit.

U.S. government bonds, which have emerged as a major concern for Wall Street and the White House, showed renewed stress, with the 10-year Treasury yield at one point jumping above 4.4 percent. (Yields move inversely to prices.)

Mr. Trump also lashed out at Mr. Powell last week, saying to reporters on Thursday that “if I want him out, he’ll be out of there real fast — believe me.

The Fed chair had warned in a recent speech that tariffs could create a “challenging scenario” by putting the central bank’s two main goals — stable inflation and a healthy labor market — in tension. As tariffs have been imposed, some surveys have shown consumers bracing for sharply higher prices.

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