Kathy Willens, Associated Press
In this Dec. 26, 2011 file photo, a woman walks down 34th Street carrying the fruits of her shopping expedition on the day after Christmas in New York.

NEW YORK — A flurry of post-Christmas bargain shopping helped drive sales higher in the last week of December, according to a report Wednesday from a shopping mall trade group. Increased gift card use, mild weather and a federal holiday on Monday all contributed.

Sales at stores open at least one year rose 5.3 percent during the week ended Saturday compared with the same period a year ago.

That report comes from the International Council of Shopping Centers and Goldman Sachs Weekly Chain Store Sales Index, which estimates sales for 24 major stores like Target Corp. and Costco Wholesale Corp.

Revenue at stores open at least a year rose 1.2 percent for the week ended Saturday compared with the previous week, according to the index.

The metric is considered a key gauge of a retailer's health because it excludes results from stores recently opened or closed.

As a result of the latest surge, the group increased its December sales growth estimate to a range of 4 percent to 4.5 percent.

Major retailers are set to release their final figures for the month on Thursday, but the big concern is how aggressive discounting and other incentives like earlier store openings and free shipping affected merchants' profits.