Europe's medicines regulator has been stopped from releasing clinical trial data about drugs made by AbbVie and Intermune, following a court ruling favouring the two U.S. companies.

The European Medicines Agency said on Tuesday it intended to appeal the interim decision by the European Union's general court.

The court action, which prevents the European Medicines Agency (EMA) from releasing documents until a final ruling is given, highlights the battle between campaigners for more transparency and companies who fear it will harm their business.

The London-based watchdog has been on a collision course with some drugmakers since deciding it would lift the lid on previously secret clinical trial data that is submitted by companies as part of the application process for new drugs.

Since November 2010, the EMA has released 1.6 million pages of detailed clinical trial information - an approach it says reflects growing public demands for more openness to ensure that drugmakers cannot conceal adverse drug effects.

Its policy was challenged, however, by both AbbVie and Intermune, which sought an injunction in cases relating to requests for the release of data about their drugs.

In the case of AbbVie, information had been sought about its rheumatoid arthritis drug Humira, the world's top-selling medicine. One of those seeking the data was UCB, a rival Belgian drug company.

The Intermune case related to information that was sought by academic researchers.

An AbbVie spokeswoman said the U.S. company supported transparency of clinical research for the benefit of patients, but was concerned that commercially confidential information contained in EMA filings could be used by other companies to compete against its product.

In a move that has alarmed a number of pharmaceutical companies, the EMA plans to step up transparency further from next year by establishing a systematic process for the release of full clinical trial data.