Speaking by video conference with European leaders gathered in Paris, Trump also said "Europe must stop purchasing Russian oil that is funding the war," a senior White House official told AFP on condition of anonymity.

Ukraine's President Volodymyr Zelensky, who also took part in the meeting, said earlier that Trump is "very dissatisfied" with European purchases of Russian oil, saying the buyers were Hungary and Slovakia.

Zelensky also said he discussed sanctions on Russia and protecting Ukraine's airspace in the call that he and European leaders held with Trump.

Trump, whose efforts to mediate between Russia and Ukraine have failed to produce a breakthrough, has been tightlipped on what his next move will be as he seeks an end to the war.

The United States has already decided to impose sanctions on India as punishment for buying Russian oil.

Trump so far has not done this with China, which imports a lot of Russian oil and is holding trade talks with Washington.

Trump has been talking tough of late about China, however.

On Tuesday he accused Chinese President Xi Jinping of conspiring against the United States with Russian President Vladimir Putin and North Korean leader Kim Jong Un when the three gathered in Beijing to watch a big military parade commemorating the end of World War II.