EU officials have pressured VW to do more to compensate European customers after it admitted to U.S. regulators in September 2015 that it had cheated on emissions tests there using software installed in as many as 11 million diesel vehicles sold worldwide - the majority of them in Europe.

Agencies from the EU's 28 member states and the European Union executive reiterated concerns that the German auto giant has not done enough to respond to a request it improve consumer information on the repairs, speed up the process and pledge to fix any problems arising after the repair.

Actions taken by VW on the 8.5 million car recalls made in the bloc "so far resulted in positive developments," the EU said in a statement. The repair rate has almost reached 80 percent of all affected cars in Europe, it said.

But it added that: "Volkswagen has not provided a full and clear guarantee that the update is not affecting the cars' performance and has refused to simplify the conditions giving access to the Trust Building Measure."

Pushing VW to admit wrongdoing, consumer protection authorities asked the carmaker "to make it clear that the use of that particular software was prohibited according to EU-law."

"On the reason for the repair, Volkswagen is not clear enough," they said.

Despite VW's admission of harm to consumers in the United States, it says it has not broken the law in Europe and sees no need to offer similar compensation to consumers there.