Mexico's manufacturing activity has started to reflect the economic slowdown in the United States, with a further drop in activity likely if the U.S. economy remains lackluster, a business group said.

"If the slowdown in the United States is prolonged, manufacturing growth in Mexico could be seriously compromised," the Mexican Finance Executives Institute, or IMEF, said.

The business group, which includes executives and specialists from financial institutions in Mexico, said its IMEF Manufacturing Index fell by 3.1 points in July to 50.4.

The drop "suggests that Mexico's economic activity has started to decelerate, following the trend in the United States," IMEF said.

The high level of integration between Mexican and U.S. manufacturing "makes it practically inevitable that the U.S. slowdown will be reflected in economic activity in Mexico," IMEF said.

The IMEF Non-Manufacturing Index, which tracks trade and services, fell by just 0.1 points last month, "suggesting that trade and services have continued at moderate levels, not yet reflecting the slowdown seen in manufacturing activity," the business group said.