Russia’s declining revenue is hampering its ability to finance Ukraine.

Russia’s revenue from fossil fuel exports collapsed in December, according to a new report, significantly hampering President Vladimir Putin’s ability to finance the war in Ukraine.

The findings, Ukrainian officials and campaigners say, illustrate the effectiveness of targeting Russia’s oil revenue and underscore the urgent need for Western policymakers to ratchet up the financial pressure on Moscow in order to help Kyiv prevail.

Published Wednesday by the Centre for Research on Energy and Clean Air, an independent Finnish think tank, the report found the first month of the European Union’s ban on seaborne imports of Russian crude and the G-7′s price cap had cost Moscow an estimated 160 million euros ($171.8 million) per day.

Ukraine war: Moscow's invasion likely to inflict long-term economic decline on RussiaWATCH NOW

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Ukraine war: Moscow’s invasion likely to inflict economic decline on Russia

CREA’s report said the Western measures were largely responsible for a 17% fall in Russia’s earnings from fossil fuel exports in the final month of 2022. It means that Russia — one of the world’s top oil producers and exporters — saw revenue from fossil fuel exports slump to its lowest level since Putin launched his full-scale invasion of Ukraine in late February.

“The EU’s oil ban and the oil price cap have finally kicked in and the impact is as significant as expected,” Lauri Myllyvirta, lead analyst at CREA, said in a statement.

“This shows that we have the tools to help Ukraine prevail against Russia’s aggression. It’s essential to lower the price cap to a level that denies taxable oil profits to the Kremlin, and to restrict the remaining oil and gas imports from Russia,” Myllyvirta said.

The Group of Seven, Australia and the EU implemented a $60-per-barrel price cap on Russian oil on Dec. 5. It came alongside a move by the EU and U.K. to impose a ban on the seaborne import of Russian crude oil.