As European Union leaders gather this week with US President Joe Biden for a series of summits aimed at hardening the West’s response to Russia’s invasion of Ukraine, they will consider imposing an oil embargo on Russia.

In order to force Russian President Vladimir Putin’s military withdrawal from Ukraine, the EU and its Western allies have already imposed a slew of punitive sanctions, including the freezing of the Russian central bank’s assets.

“We are working on a fifth round of sanctions and many new names are being proposed,” a senior EU diplomat said on condition of anonymity because the discussions are not public.

EU governments will take up the discussion among foreign ministers on Monday, before Biden arrives in Brussels on Thursday for summits with NATO’s 30 allies, as well as the EU and in a Group of Seven (G7) format including Japan.

The Kremlin has so far not been moved to change course in Ukraine by four rounds of EU sanctions imposed over the past three weeks, including on 685 Russians and Belarusians and on Russian finance and trade.

That leaves the bloc with the economically toughest choice of whether to target Russian oil, as the United States and Britain have done but not the 27-nation EU, given its dependence on Russian gas for energy.

Diplomats told Reuters that Baltic countries including Lithuania are pushing for an embargo as the next logical step, while Germany is warning against acting too quickly because of already high energy prices in Europe.

Russia invaded Ukraine on Feb. 24. Putin has called Russia’s actions a “special operation” meant to demilitarize Ukraine and purge it of what he sees as dangerous nationalists. Ukraine and the West say Putin launched an aggressive war of choice.