Vacancies at U.S. strip malls and regional malls rose, while rental rates fell as more retailers downsized or shut down in the second quarter, Reuters reported.

According to Reis Inc., a real estate research firm, vacancy rates at U.S. strip malls reached 10 percent, a 17-year high, in the second quarter and regional mall vacancies rose to 8.4 percent, a nine-year record.

About 7.9 million square feet of space came on the market during the second quarter, the second-largest figure ever recorded, but down from the all-time high of 8.1 million square feet in the first quarter.

Meanwhile, the average asking rent at strip malls fell 1.7 percent from a year ago to $19.28 per square foot. When months of free rent and other concessions are factored in, the effective rental rate fell 3.2 percent to $17.01.

Rents at regional malls fell 2.9 percent to $39.42 per square foot from second quarter 2008.

Lower rates could make it harder for mall owners to meet loan payments and could increase the rate of defaults within the retail real estate sector.