An illustration picture shows the logo of car-sharing service app Uber on a smartphone next to the picture of an official German taxi sign September 15, 2014. REUTERS/Kai Pfaffenbach/Illustration/File Photo

ABU DHABI (Reuters) - Ride-hailing companies Uber [UBER.UL] and Careem have suspended services in Abu Dhabi, the capital of the United Arab Emirates, since Saturday and do not know when they can resume operations, they said on Sunday.

The National, a UAE newspaper, quoted unnamed sources as saying that as many as 50 drivers for Uber and Careem had been arrested.

An Abu Dhabi source familiar with the situation told Reuters some drivers had been detained over violations of regulations, but did not specify how many drivers or describe the violations.

“This is a temporary suspension and we will let you know of any further updates,” an Uber spokesman in Dubai said via email. He did not respond to questions about the arrests or the reason for the suspension of services.

Christian Eid, vice-president of marketing and communications for Careem, a Dubai-based company, said many of its drivers were being stopped by authorities in Abu Dhabi, apparently over licensing issues, and as a result had become nervous and were staying off the roads. This had forced Careem to halt services there, he said.

The Abu Dhabi government’s Center for Regulation of Transport by Hire Cars, which manages the taxi and transport sector, did not respond to queries. The center oversees about seven taxi operators and 18 limousine operators, some of which are partly government-owned. Abu Dhabi police did not respond to requests for comment.

Uber and Careem said they had not suspended operations in neighboring Dubai, the commercial and tourist hub of the UAE. The emirate of Abu Dhabi has a population of about 2.8 million and Dubai has roughly 2.5 million.

Uber, which launched services in Abu Dhabi in 2013, said last year that the Middle East and North Africa contained some of its fastest-growing markets and that it planned to invest $250 million to expand in the region.