Two surveys of weekly chain-store sales showed mixed results at the height of the holiday shopping season.

The International Council of Shopping Centers, or ICSC, said its Weekly Chain Store Sales Index, a collaboration with UBS, rose 3.5% in the third week of December, compared with last year. That marks the index's strongest results so far for the season, up from the 2.4% pace set in the second week of the month and the 3.3% logged in the first.

For the holiday season, ICSC continues to expect that sales will grow by 2.5% to 3%.

"With just a few days left before Christmas, consumers continued to pick up their holiday shopping and gave retailers another week of positive sales," said Michael Niemira, ICSC's chief economist and director of research. "Consumers have stated that they have been shopping even later this holiday season than last year, which provides some evidence that this season will have a late, last-minute surge."

As of Dec. 19, only 31% of consumers had completed their gift shopping, which means that some 70% still have at least a little shopping left before Christmas, according to the report.

Separately, Redbook Research said Tuesday that its weekly Johnson Redbook Retail Sales Index rose 2.1% in the week ended Dec. 18, compared with the same week last year. That follows a 2% gain in the previous week, and December's results are currently down 0.7% from November's. So far this month, sales are adding 2% compared with last year, down from the target rate of 2.6% growth.

"Sales continued below plan for the third consecutive week and are making it harder for retailers to meet targets," said Redbook Research in a release.

The firm said high-priced items, such as designer handbags and housewares, were volume leaders at upscale department stores, while discounters reported an improvement in electronics like iPods, digital cameras and satellite radios.

The two main factors working to move merchandise are a big increase in promotional discounting along with the onset of colder weather, which has spurred sales in seasonal items like outerwear, heavier apparel and other cold weather products.

"Some sources said markdowns had become persuasive and were affecting margins," the firm said. "In addition, online shopping remained at a strong pace and gift cards were on the rise, shifting sales to the period after the holiday season, which could affect sales data."