US retail sales fell sharply in December, the biggest holiday shopping month of the year, according to Commerce Department data published today. 

Sales of retail and food services dropped 0.9% from November, and the previous two months' gains were revised lower, suggesting weakness in consumer spending that accounts for about 70% of US economic output. 

The December drop in sales surprised analysts, who on average had penciled in a modest 0.1% increase. 

Stripping out a 0.7% fall in motor vehicles and parts sales, retail sales fell 1% in December, instead of the 0.1% rise expected. 

A steep fall in petrol prices helped to lower the headline retail sales number, in data that is not adjusted for price changes. Sales at the pump plunged 6.5%. 

But other categories saw declines during the Christmas shopping season, despite the lower petrol prices that left more money in consumers' pockets. 

Sales dropped in miscellaneous and general merchandise stores, clothing stores and sporting goods, hobby, book and music stores. 

Building materials sales fell, and even online sales, which have put in a solid showing this year, fell 0.3% after a strong gain in November. Food services and bars, as well as furniture stores, saw increases in sales last month. 

US retail sales data offers a snapshot on consumer spending, the bulk of which is spent on services. 

Analysts pointed out that the Commerce Department's December report on consumer spending, due on February 2, will give a clearer idea of the strength of the US economy heading into 2015.