The World Trade Organization will issue a confidential final ruling on January 31 concerning European claims that Boeing benefited from unfair aircraft subsidies, sources familiar with the case said on Friday.

The report, which will not be made public for several weeks, is the latest round of legal ping-pong between the European Union and United States over mutual claims their aircraft industries have been unfairly shielded from competition.

The EU claimed victory after a confidential interim report found in September that Airbus rival Boeing had received several billion dollars of aid, but the two sides disagreed publicly over the severity of the judgment.

That ruling followed WTO condemnation last June of illegal European subsidies for Airbus, mostly in the form of government launch-aid loans. These findings came in an earlier case brought by the United States, which is now the subject of appeal.

The transatlantic subsidy row is the biggest bilateral dispute ever at the Geneva-based trade body.

The final report on the EU case against the United States was expected to be distributed to the parties late afternoon Geneva time on January 31, the sources said.

The WTO declined to comment.

Historically, final WTO rulings have made few if any substantial changes to interim findings.

(Reporting by Tim Hepher; editing by Sophie Walker)