Boeing facilities are seen in Los Angeles, California, U.S. April 22, 2016. REUTERS/Lucy Nicholson/File Photo

GENEVA (Reuters) - The United States appealed on Friday against a ruling on tax breaks for Boeing, the World Trade Organization said on its website, the latest step in a more than a decade-old transatlantic spat over subsidies for Boeing and Airbus.

A panel of WTO adjudicators ruled last month that a tax break from Washington state to help U.S. planemaker Boeing BA.N develop its new 777X jetliner was a prohibited subsidy.

Details of the appeal were not immediately available, but Boeing said last month that it was confident that the United States would be able to reverse the ruling.