Energy giant Shell says the world doesn't have systems to trace Russian oil refined overseas. This could undermine sanctions.

The European Union is planning to ban Russian oil, but it is not the only country that is banning Russian oil.

Ben van Beurden, chief executive of Shell, said on Thursday that it is not possible to identify the origin of any crude, including Russian, once it has been refined somewhere else.

He told reporters on a quarterly earnings call that there were no systems in the world to trace back the origin of that molecule.

The difficulty of enforcing sanctions against Russian oil in global supply chains is highlighted by Van Beurden.

The EU proposed a ban on Russian oil imports as part of a sixth package of sanctions against the country. Diesel and jet fuel from Russia will be subject to the measures, but not products refined with Russian crude elsewhere.

Diesel coming out of an Indian refinery that was fed with Russian crude is considered to be Indian diesel, van Beurden said.

He said it was difficult to trace back what exactly is or isn't Russian.

He said that Shell does not refine products that use Russian oil.

He said that Shell doesn't deal with Russian counterparties and doesn't buy material from the country on the spot market. The company plans to exit Russian contracts by the end of the year.

The energy giant is writing off up to $5 billion in assets after pulling out of the Russian oil and gas sector.