With blanket American tariffs on Canada, China, and Mexico set to come into force Saturday against a background of already-stubborn inflation, stock prices slid in the final hour of Wall Street trading Friday.

The mood was soured by the flat denial by the White House of a report that President Trump would delay the levies by a month. The Standard & Poor’s 500, which was higher at midday, ended down 0.5 percent at 6,040.53, while the Dow Jones industrial average dropped 0.75 percent and the Nasdaq composite lost 0.28 percent.

Bond prices fell, driving up the yield on the 10-year Treasury bond to 4.58 percent from 4.53 percent on Thursday and about the same as the level at the end of last year, according to CNBC. The tariffs could lead to higher prices for imports from the three trading partners, putting upward pressure on inflation, which has remained above the Federal Reserve’s 2 percent annual target.

The dollar edged up against foreign currencies. The value of the greenback, though, lurked essentially at record lows, barely below, at deadline, a 2,800th of an ounce of gold. With the central bank’s latest easing cycle evidently on pause, the target of between 4.25 percent and 4.5 percent for overnight interest rates is supportive for the greenback.

Mr. Trump plans to impose 25 percent tariffs on imports from Mexico and Canada, which he has said are not doing enough to halt the flow of undocumented migrants into America. He is also slapping a 10 percent penalty on Chinese imports as punishment for facilitating fentanyl distribution in America.