China has barred Russia’s airlines from flying foreign-owned jetliners into its airspace, the Russian news outlet RBK reported, after President Vladimir Putin threw the aircrafts’ ownership into doubt by allowing them to be re-registered in Russia to avoid seizure under sanctions over Moscow’s attack on Ukraine.

The European Union, home to major aircraft leasing companies, banned the sale or lease of aircraft to Russian carriers in February. Putin responded by approving the re-registration measure in March, which prompted suggestions foreign owners may never recover planes worth billions of dollars.

China’s air regulator asked all foreign carriers last month to update ownership information and other details, RBK said, citing two unidentified sources. It said Russian airlines that couldn’t provide documents showing their aircraft were “de-registered abroad” were barred from Chinese airspace.

The Civil Aviation Administration of China didn’t immediately respond to a request for confirmation and details of the decision.

President Xi Jinping’s government said in February it has a “no limits” friendship with Moscow but has tried to distance itself from Putin’s war. Beijing has criticized Western sanctions but appears to be avoiding steps that might be seen as helping Moscow for fear of possible penalties against Chinese companies.