• Firms in Greece, Cyprus, and Malta have shipped more Russian oil since the Ukraine war started.

• Freight rates for oil tankers have tripled since Russia invaded Ukraine on February 24.

• The rise in Russian oil shipments undermines intensifying sanctions against the country.

Shipping companies in the European Union's three largest maritime nations of Greece, Cyprus, and Malta have doubled the quantity of Russian oil they transport since the invasion of Ukraine on February 24, The Independent reported on Monday.

Shipping companies and vessels linked to the three countries moved an average of 58 million barrels of Russian oil in the month of May, the UK media outlet reported, citing an analysis from Global Witness, a non-government organization. That's almost double the 31 million barrels they collectively transported in February. The three countries have the largest shipping fleet in the EU, according to Reuters.

The jump in the transportation of Russian crude came on the back of a tripling in oil tanker freight rates since the invasion of Ukraine on February 24 — and it's undermining EU sanctions against Russia.

"Ships linked to Greece, Cyprus and Malta are making a mockery of the EU effort to sanction Putin's war machine, keeping cash flowing to Russia as the country's armed forces continue to pummel Ukraine," Louis Goddard, a senior data investigations adviser at Global Witness, told The Independent.

The NGO's report follows findings by London's Sunday Times that Greek shipping companies are taking part in "ship-to-ship" transfers of Russian oil to mask the transportation of the fuel. Data reviewed by the Sunday Times pointed to an increase in such movements, which involves a Russian ship unloading oil to another vessel from a neutral party, the outlet reported on Sunday.

There is no suggestion that the companies and ships involved in transporting Russian oil are breaching sanctions, The Independent and Sunday Times reported.

Last Monday, the EU agreed on a Russian oil ban that stands to cut about 90% of Russian oil imports to the bloc by the end of the year. That was after the EU reportedly scrapped plans to stop EU-owned ships from transporting Russian oil to countries outside the region, such as China and India.

However, the EU and the UK are planning to deter the practice by not allowing ships carrying Russian oil to take out insurance — which is crucial for the shipping industry, the Financial Times reported last week.

Global Witness did not immediately respond to Insider's request for the report, which was sent outside regular business hours.