Disappointing Amazon results and rising fears about the Delta variant of the novel coronavirus caused US equities to pull back Friday from the run of gains in recent days.
Analysts said investors also may be taking advantage of recent high prices to score some profits.
In the final session of the month, Dow Jones Industrial Average was down 0.4 percent at 34,954.52 in late morning trading.
The broad-based S&P 500 lost 0.6 percent to 4,393.91, while the tech-rich Nasdaq Composite Index tumbled 0.8 percent to 14,657.35.
The Amazon earnings report "was disappointing and basically is dragging everything down," said Peter Cardillo of Spartan Capital.
But he told AFP: "We are at high level, it's the end of the month, and stocks performed nicely during the month of July, so the investors are taking some money off the table."
Amazon lost seven percent after missing revenue forecasts and offering lower-than-expected projections for the coming quarter.
ExxonMobil fell two percent and Chevron dipped one percent after reporting surging profits, while Procter & Gamble rose 2.9 percent despite noting that sales growth will slow amid rising costs.
Inflation concerns could be a limiting factor on growth, and government data Friday showed a key US measure -- the personal consumption expenditures (PCE) price index -- posted a 12-month increase of four percent in June, which was high but did not pick up speed from the prior month.
The Covid-19 pandemic remains a concern, as the spread of the Delta variant caused some areas of the US to restore indoor mask mandates.
The Washington Post cited a document from the Centers for Disease Control indicating the new variant is more infections and more serious than earlier ones, and vaccinated people appear to transmit it as easily as the unvaccinated.