A World Trade Organization report on aid for European planemaker Airbus, expected to condemn the European Union for illegal subsidies, will be published on June 30, trade sources said on Friday.

The 1,000-page report was issued confidentially to the European Union and United States in March, and sources familiar with it said at the time a panel of WTO experts had found some of the aid challenged by the United States was prohibited export subsidies and must be stopped within 90 days.

They said the document, the latest stage in a decades-long transatlantic dispute over the multi-trillion-dollar market for large passenger aircraft, would back many of the U.S. complaints.

The EU is likely to appeal against the ruling, delaying the point at which it takes force. Brussels says the Airbus findings are only part of the picture and it is premature for one side to claim victory.

The WTO is expected to issue an initial confidential report to the parties in a countersuit brought by the EU against the United States over support for Airbus rival Boeing next month.

Boeing hopes the report on Airbus will stop the EU from subsidizing the new A350 plane, which will compete with the U.S. company's 787 Dreamliner.

Boeing and Airbus parent EADS are competing for a $50 billion contract to supply the U.S. Air Force with new tankers. The EADS offering is based on the Airbus A330, one of the planes that received aid challenged by the United States.

(Editing by Stephanie Nebehay and Andrew Dobbie)