U.S. car service Uber is planning an aggressive expansion in Germany despite a backlash from cities like Berlin and Hamburg, which have questioned its right to operate in highly regulated markets dominated by traditional taxis.

The San Francisco-based company, which allows users to summon rides on their smartphones, announced late on Tuesday that it was experiencing "huge demand" for its services in German cities where it is not currently operating.

It plans to move into Cologne and Stuttgart later this year, and is also eyeing Nuremberg, Bonn, Essen, Dortmund and Potsdam. From now until the end of the year, it expects to double the number of subscribed users in Germany, after growing fivefold so far in 2014, the company said.

Currently, Uber is operating in Berlin, Hamburg, Munich, Frankfurt and Duesseldorf. But it has run into trouble in the German capital and northern port city of Hamburg, which have banned the service over concerns that drivers lack licenses to carry passengers and do not have full insurance coverage.

Uber appealed the rulings and has carried on operating in the two cities pending a final verdict. Other German cities are also considering a ban, according to media reports.

Founded in 2009 and valued at $18.2 billion based on its latest funding round in June, Uber Technologies Inc describes itself as a marketplace that puts people in contact with each other, not a transportation service.

Drivers have to be over a certain age, have a valid driving license, and undergo background checks before they can pick up passengers.

Uber has faced regulatory obstacles in a number of European cities as well as legal challenges from taxi companies hoping to keep new competition out. Taxi drivers across Europe caused chaos in June by protesting against the service.

Earlier this month, a Paris court demanded that Uber change its invoicing system.

(This story corrects last paragraph to say Paris court did not impose a ban on Uber)

(Reporting by Ludwig Burger; Editing by Noah Barkin)