The United States will shift its focus to targeting those trying to avoid the "major" sanctions it has waged against Russia, its national security advisor said Thursday.

Washington and its allies have responded with fury to Moscow's attack on Ukraine, sanctioning Russia's financial system, aviation sector and other major parts of its economy in a thus-far fruitless effort to get President Vladimir Putin to back down.

"We feel we've taken the major measures but where our focus will be over the course of the coming days is on evasion," Jake Sullivan said during a symposium.

"We'll have some announcements in the next week or two that identify targets that are trying to facilitate that evasion both inside Russia and beyond," he said.

Last month, the United States announced they were cutting off imports of Russian oil, gas and coal.

The European Union, meanwhile, remains divided over a potential ban on Russian energy imports. 

Some in the bloc, notably Germany, have been reluctant to hit all energy exports because of the damage it would do to their own economies.

"Of course, there's this issue of energy in Europe, and that's an ongoing conversation," Sullivan said.

He also touched on the assets of Russian oligarchs which have been frozen by the sanctions, stating that as far as yachts and other effects were concerned, "our goal is not to give them back."

"There are authorities we have, and there are further authorities that maybe we could develop, and that's something we're actively looking at," Sullivan said.

Some in the US Congress have already called for the sale or liquidation of Russian assets caught up in the sanctions, with proceeds to be used for the reconstruction of Ukraine after the war.