The World Trade Organization ruled Tuesday that the European Union could impose tariffs worth $4.0 billion on US imports in retaliation for illegal American aid to plane maker Boeing, a year after the EU was sanctioned for its support of Airbus.

The decision was the latest development in a 16-year saga between Washington and Brussels over support for their leading civil aircraft manufacturers.

The WTO determined that that amount was "commensurate with the degree and nature of the adverse effects determined to exist" from US support for Boeing considered to be in violation of international trade rules, according to the 121-page arbitrator's report.

According to a list of targets seen by AFP, the European Union is expected to impose tariffs on aircraft made in the United States, along with tractors, sweet potatoes, peanuts, frozen orange juice, tobacco, ketchup and Pacific salmon.

The EU's top trade official signalled a preference for avoiding new tariffs, calling instead on Washington to withdraw US levies on European goods after the WTO last year authorised a record $7.5 billion in US sanctions against European goods.

Washington then imposed punitive tariffs of 25 percent on EU products such as wine, cheese and olive oil. A 10-percent tariff on Airbus planes was hiked to 15 percent in March.

"I have made it clear that my strong preference is for a negotiated settlement with the US, avoiding harmful rounds of measures and countermeasures," EU executive vice president Valdis Dombrovskis said.

"Our suggestion is that the US withdraws the tariffs they imposed as a consequence of the Airbus ruling," the former Latvian prime minister added.

US Trade Representative Robert Lighthizer said Tuesday the US would "intensify" talks to find a resolution to the longstanding dispute.

"The United States is determined to find a resolution to this dispute that addresses the massive subsidies European governments have provided to Airbus and the harm to US aerospace workers and businesses," Lighthizer said.

Additional tariffs on Boeing aircraft that the EU will be able to impose will make it more difficult for the US aircraft maker to restart European sales of its 737 MAX once the plane is cleared to retake to the skies
Additional tariffs on Boeing aircraft that the EU will be able to impose will make it more difficult for the US aircraft maker to restart European sales of its 737 MAX once the plane is cleared to retake to the skies AFP / Jason Redmond

"We are waiting for a response from the EU to a recent US proposal and will intensify our ongoing negotiations with the EU to restore fair competition and a level playing field to this sector."

Lighthizer said the ruling clearing the way for $4 billion in EU tariffs on American goods had "no valid basis" because it was based on a tax provision by Washington state, where Boeing is based, that had been repealed earlier this year.

Following Tuesday's decision, the EU must request permission from the DSB to apply the decision -- something it could do at the body's next meeting on October 26, a week before the US presidential election.

While several EU leaders have been calling for imposing the tariffs immediately if Washington does not agree to drop its levies, few expect it to do so.

One industry source however expects the WTO ruling to "open the door for negotiations".

Given the crisis the airline industry now finds itself in and the effect that is having on Airbus and Boeing, a long drawn-out battle in which tariffs raise the prices of aircraft does not serve the interests of either the EU or the United States.

Airbus was among those calling for a settlement.

"It is time to find a solution now so that tariffs can be removed on both sides of the Atlantic," said Airbus CEO Guillaume Faury.