The World Trade Organization has backed a U.S. complaint that European governments provided illegal subsidies for EU-based Airbus jet aircraft.

The WTO issued its confidential, interim decision on Friday to government trade officials in the U.S. and the EU.  The ruling is subject to a lengthy appeals process that Airbus said could take up to five years.

The case grew out of complaints by U.S.-based Boeing that European nations subsidize Airbus with tens of billions of dollars in cheap loans. The U.S. argued the aid has allowed the firm to cut costs and give its planes an unfair price advantage.

Meanwhile, the WTO is expected to decide next year on a counter-claim filed by Airbus that billions of dollars in U.S. government contracts for space and military research and development give Boeing an unfair subsidy.

The cases between the world's two largest aircraft builders are the largest ever to come before the WTO.

EU officials have told the Bloomberg financial news service that today's ruling only covers past aid to the Airbus A380, launched in 2000.  Officials said the EU would continue to subsidize production of the planned A350 aircraft.

Boeing also has plans to launch a new plane, the 787.

Aviation experts have said that new commercial aircraft programs are so expensive that most rely on some government backing.

Some information for this report was provided by AFP and AP.