President Joe Biden plans to announce new sanctions against Russia on Thursday while in Brussels for meetings with NATO and European allies, according to a top national security aide.

Biden, who will take part in a special meeting of NATO and address the European Council summit, is also expected to underscore efforts to enforce the avalanche of existing sanctions already announced by the U.S. and allies.

“He will join our partners in imposing further sanctions on Russia and tightening the existing sanctions to crack down on evasion and to ensure robust enforcement,” said White House national security adviser Jake Sullivan, who declined to further preview new sanctions the president will announce.

Biden is traveling to Brussels and Poland — which has received more than 2 million Ukrainian refugees who have fled since the Feb. 24 invasion — looking to press for continued unity among Western allies as Russia presses on with its brutal invasion of Ukraine.

In Poland, Biden will meet with Polish President Andrzej Duda, who has requested further U.S. aid and a stepped up military presence on NATO's eastern flank as the war grinds on. The U.S. has already added several thousand U.S. troops to it regular presence. Estonia, Latvia, Lithuania and Romania have also called for a greater NATO or U.S. military presence in recent weeks.

Sullivan suggested more help will be coming with announcements by Biden “on longer term adjustments to NATO force posture on the eastern flank.”

“We feel that it is the right place for him to go to be able to see troops, to be able to see humanitarian experts and to be able to meet with a frontline and very vulnerable ally,” Sullivan said of Biden's visit to Poland.

Biden and NATO have said repeatedly that while the U.S. and NATO will provide weapons and other defensive support to non-NATO member Ukraine, they are determined to avoid any escalation on behalf of Kyiv that risks a broader war with Russia.

Polish leaders have called for a Western peacekeeping mission to intervene in Ukraine, a step that the U.S. and other allies worry could lead to a broadening of the war.

Sullivan added that Biden will also “announce joint action on enhancing European energy security and reducing Europe’s dependence on Russian gas."