Markit Economics released its preliminary services purchasing managers' index (PMI) for the U.S. on Tuesday. The U.S. preliminary services purchasing managers' index (PMI) declined to 55.2 in August from 55.7 in July, missing expectations for an increase to 56.0.

A reading above 50 indicates expansion in economic activity.

The decline was driven by a weak new business growth.

"Service providers' new business volumes expanded at the slowest pace since January, suggesting that underlying momentum within the U.S. economy had shifted down a gear even before the recent global market turmoil and escalating worries about China's growth outlook gathered on the horizon.," Markit Senior Economist Tim Moore.