Escalating global trade tensions are starting to make Americans nervous.

The University of Michigan's monthly confidence index, a widely used gauge of consumer sentiment, fell slightly in July from the previous month.

Although consumers remain bullish on their prospects amid low unemployment, concerns are growing about the U.S. trade dispute with China other countries.

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"The darkening cloud on the horizon... is due to rising concerns about the potential negative impact of tariffs on the domestic economy," Richard Curtin, chief economist of the survey, said in a statement.

Negative concerns about the impact of tariffs have recently accelerated, rising from 15 percent in May, to 21 percent in June, and 38 percent in July, according to the findings.

Among the top third of income earners, who account of half of U.S. consumer spending, 52 percent had negative views on the impact of tariffs on the domestic economy.

Despite these jitters, solid economic growth kept the U. of Michigan index near its highs.

"We view this as a return to trend, indicating still upbeat consumers enjoying a broadening jobs market, firming wage growth and still-accommodative interest rates," Oxford Economics said in a client note.