The holiday shopping season has gotten off to a "very strong" start, according to the largest U.S. retail trade group.

The National Retail Federation said Tuesday that consumer spending has been strong, fueled by a better economy and stores' investments in online services including features that allow shoppers to buy online and pick up the items at the store.

The trade group's assessment comes even after a survey of more than 3,000 shoppers Thanksgiving and Friday forecast that fewer people would turn out for the five-day weekend that ended Monday, compared to a year ago.

This year, there were more than 165 million people who shopped online or in stores from Thanksgiving through Cyber Monday, based on survey results. Last year, that figure was 174 million. The retail group attributed the drop to stores spreading out their deals beyond the Black Friday weekend.

"This was a very strong holiday weekend," said Bill Thorne, a spokesman at the trade group.

The group now says it expects sales for November and December will be at the high end of its earlier forecast of a 4.3 to 4.8 percent rise. That would be below last year's 5.3 percent increase but well above the average annual increase of 3.9 percent of the past five years.

Meanwhile, Adobe Analytics, which tracks online spending, said that Cyber Monday was expected to have hit $7.9 billion, up 19.7 percent from last year.

Thanksgiving Day generated $3.7 billion in online spending, up 28 percent, while Black Friday brought in $6.2 billion, a 23.6 percent increase from a year ago, according to Adobe.

Mobile devices accounted for 51.4 percent of site visits and 34 percent of revenue on Cyber Monday. So far, the period from Nov. 1 through Monday has generated online sales of $58.5 billion, up 19.9 percent, Adobe said.