(Adds confirmation by Volkswagen of America and background)

BERLIN, Jan 6 (Reuters) - A senior U.S. sales manager has quit Volkswagen’s North America operations just as the carmaker’s deliveries in the world’s second-largest auto market fall steeply.

Ron Stach, senior vice president of sales at Volkswagen of America, has left the automaker, a spokesman for VW in the United States said on Saturday, confirming a report by Automotive News.

He declined comment on the reason for Stach’s departure. A spokesman at VW’s global headquarters in Wolfsburg didn’t return calls seeking comment.

Stach, who joined VW’s North America operations in 2006 and previously worked at Mazda Motor Corp’s division in the region, couldn’t be reached for comment.

VW said last Wednesday that its U.S. sales rose 5.2 percent to 339,676 brand models last year but plunged 19 percent in December after posting their first monthly drop in 2017 in November.

The world’s largest automaker by sales is keen to end losses in the United States by the end of the decade, counting on a series of higher-margin new models and structural changes as it struggles to draw a line under its diesel emissions test cheating scandal which broke in the United States in 2015.

Stach became vice president of sales in March 2016, the same month that Michael Horn, the carmaker’s then-CEO of North American operations, resigned.

During VW’s initial response to the emissions scandal, Horn was the carmaker’s public face in the United States, apologising days after the scandal became public on Sept. 18, 2015 and testifying before Congress.

Stach will be replaced temporarily by Derrick Hatami who joined VW of America last June as executive vice president for sales and marketing, VW said. (Reporting by Andreas Cremer; Editing by Stephen Powell and Adrian Croft)