Dialing in to talks between United States and European Union officials, President Donald Trump raised the possibility of tariffs between 50 percent and 100 percent on oil buyers such as China and India, said the official, who was not authorized to discuss these details publicly.

The talks come as EU sanctions envoy David O'Sullivan, who has spearheaded the bloc's global outreach on preventing Moscow's evasion of sanctions, is leading a delegation in Washington for meetings on Monday and Tuesday.

Trump dialed in for discussions Tuesday alongside Ukraine's prime minister, the US official said.

"The source of the money for the Russian war machine is oil purchases by China and India," the official added. "If you do not get at the source of the money, there's no way to stop the war machine."

Also involved in talks were Treasury Secretary Scott Bessent and officials from the US Trade Representative's office and State Department.

But the government official stressed that although Trump is "ready to go," he believes that "the EU has to be with us."

Another US official referred to a bill with 85 Senate co-sponsors that would authorize Trump to impose secondary tariffs on countries trading with Russia -- but questioned if the European Parliament "has the political will" to step up economic pressure via tariffs.

Besides potential tariffs, which were Trump's preferred option, officials also discussed the issue of immobilized Russian sovereign assets.

Trump on Sunday had threatened to impose more sanctions on Russia, after the Kremlin unleashed its biggest-ever aerial barrage at Ukraine.

He has also threatened to penalize countries that buy Russian oil, seeking to cut off a key revenue source for Russian leader Vladimir Putin's war. But so far, he has only hit India with so-called secondary sanctions.

"We want to get serious. We want to get this war over with, and so we're strongly encouraging our European friends to get moving," the US official said Tuesday.

The EU is preparing a fresh round of sanctions on Russia, marking its 19th since Moscow's invasion in 2022. It has said that this should include more secondary sanctions targeting countries that help Moscow avoid punishment.

Germany and France are pushing to target Russian oil giant Lukoil as part of the new round of EU sanctions, diplomats said Monday.

Bessent wrote in a post on X after Monday's meeting that "all options remain on the table" as part of Trump's strategy to support peace negotiations between Moscow and Kyiv.

The Treasury Department did not immediately have a comment on Tuesday's talks.