"Unlike past direct sanctions, secondary tariffs extend US reach globally, targeting Russia's trade partners. If enforced, they could affect at least 30-40 percent of Russia's oil sales, destabilizing its economy and rippling through global energy supplies," he warned.

Russia continued its nightly bombardment of Ukrainian cities overnight into Tuesday, after President Donald Trump said the U.S. would send military equipment to Kyiv.

Trump's moves underline his growing disenchantment with Russian President Vladimir Putin over the lack of progress in U.S.-led efforts to secure a ceasefire.