European car sales fell 6.3% year-on-year in June, damping hopes of a recovery in an industry that has been pummelled by overcapacity and weak consumer demand.
Europe's car market has been in the doldrums for months, with sales plunging to a 17-year low last year.
However hopes of a recovery were raised in April when sales rose for the first time in 19 months.
That was followed by the weakest May for two decades and the decline in June suggests no let-up in the pressure on carmakers like France's Peugeot and Italy's Fiat.
Norbert Reithofer, the chief executive of German carmaker BMW, said in a newspaper interview that he did not expect a pick-up in western European markets until the middle of next year.
In its monthly report, the Association of European Carmakers said 1,175,365 cars were registered in 27 European Union countries plus those in the European Free Trade Association in June, the lowest figure for that month since 1996.
The decline in June was broadly in with the 6.7% drop in sales across the first half of 2013.
The total number of vehicles registered in the six months - 6,436,743 - was the lowest since 1993.
"Even if there is a recovery in the second half of the year, it's hard to see how it could be strong enough to offset the bad results we've registered so far this year," said Quynh-Nhu Huynh, economics and statistics director at ACEA.
The German market, which resisted much of last year's slump, shrank 4.7% in June, while sales in France and Italy fell 8.4 and 5.5% respectively, as unemployment and austerity measures curb consumer spending.
By contrast, sales in Britain remained robust, notching up a 16th straight month of gains with a 13.4% increase.
Among major carmakers, Fiat was the biggest casualty, seeing a 13.6% drop in sales, while Peugeot, which is cutting 8,000 jobs and closing a domestic plant to stay afloat, saw a 10.9% decline.
General Motors' registrations fell 9.9%, while the Volkswagen brand, Europe's biggest, slid 6.6%.
Ford Motor Co, scrapping European plants and thousands of jobs, bucked the trend with a 6.9% rise, although its year-to-date deliveries were still down 10%.
Among luxury car makers, Mercedes posted a 2% gain, powered by new models, while the BMW brand fell 7.7% and VW's Audi dropped 8.9%.