New Delhi, Mar 17 (IANS): Companies, many based in Ireland, leased 515 airplanes worth about $10 billion to Russian airlines. They may never get them back.

On Monday, Russian President Vladimir Putin approved a law switching the jets over to the Russian airplane registry, making their return very difficult, Politico reported.

In doing so, Russia is breaching the Chicago Convention, the international rules that underpin civil aviation, according to European Transport Commissioner Adina Valean.

The European Commission is working with regulatory agencies to get the jets back, she told the European Parliament on Tuesday.

But her comments are unlikely to inspire much faith from lessors.

"We are in the process to try to do our best," she said, adding: "But to be honest, we're not very trustful because when you have such abusive behavior from a country like Russia, it's difficult to say what the outcome will be," Politico reported.

The bloc has given leasing companies until March 28 to wrap up their contracts and get their planes home. However, only a few dozen airplanes have made it back to their owners -- largely those that were outside Russia when the skies closed.

The rest are in Russia and Putin's new measure moves them onto shaky legal territory, said Donal Hanley, a professor at the Institute of Air and Space Law at Montreal's McGill University.