Sales were also down 1.6 percent from the same week of 2012, the trade group said.
ICSC vice president of research and chief economist Michael Niemira said consumers "lacked the urgency to shop this past week."
"The lack of urgency added to the sales volatility throughout September and created a weak undertone for sales," Niemira said in a statement.
Niemira said that the trade group expects the September tally to show growth in the 3 percent to 4 percent range, which is below the group's previous forecast of 4 percent growth.
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