The EU said the WTO report confirmed a preliminary ruling on the case made in September. That ruling came months after the Geneva-based trade body faulted European governments for illegally supporting local aircraft maker Airbus.

“This solid report sheds further light on the negative consequences for the EU industry of these US subsidies and provides a timely element of balance in this long-running dispute,” EU trade spokesman John Clancy said in a statement.

The EU alleges that Boeing received almost $24 billion in illegal subsidies, such as research grants and free use of technology, from NASA, the Department of Defense, and the states of Illinois, Kansas and Washington. However, how much of this aid the WTO deemed illegal won’t be clear until Monday’s report is published some time this spring.

A Boeing spokesman said he hadn’t received the report yet and would comment later Monday.

The Geneva-based trade body can’t force countries to eliminate subsidies, but it can authorize retaliatory tariffs against products from countries that fail to comply with rulings. But considering past delays and future appeals in the Airbus and Boeing cases that stage is likely years away.

The United States brought the dispute to the WTO in 2004, complaining that European governments supported Airbus, a unit of European Aeronautic Defense and Space Co., with billions of euros in illegal subsidies. It filed the case after pulling out of a 1992 agreement limiting subsidies in the aviation industry. Brussels responded with a countersuit against US support for Boeing.

The WTO ruled last year that Europe’s “launch aid” to Airbus through virtually risk-free loans as well as infrastructure support, research and development funding and export subsidies from Britain, France, Germany and Spain broke international trade rules. Both the EU and the US are appealing that case, in a public battle about who received more aid.

Airbus said that the WTO ruling backs its claim that illegal subsidies received by Boeing “have a significantly greater distortive effect than the reimbursable loans” made to Airbus.

Airbus estimates that it has lost at least $45 billion through lost sales and lower prices as a result of Boeing’s subsidies.

“From today, Boeing can no longer pretend that it doesn’t benefit from generous and illegal state subsidies. It has been doing so from the start and it’s time to stop the denial,” said Rainer Ohler, Airbus’s head of public affairs and communications.

The dispute is central to future negotiations between the US and the EU on subsidies in the aviation market, which could be worth some $3 billion over the next two decades.

Airbus and Boeing are also vying to secure a $35 billion contract to sell refueling jets to the US Air Force.

Airbus said it expects the dispute to carry on for “several more years,” and that a negotiated settlement is the only way to resolve it.