US President Donald Trump's administration has prepared additional sanctions it could use to target key areas of Russia's economy if President Vladimir Putin continues to delay ending Moscow's war in Ukraine, according to a US official and another person familiar with the matter.

US officials have also told European counterparts that they support the EU using frozen Russian assets to buy US weapons for Kyiv, and Washington has held nascent internal conversations about leveraging Russian assets held in the US to support Ukraine's war effort, two US officials said.

While it is not clear whether Washington will actually carry out any of those moves in the immediate term, it indicates that the administration has a well-developed toolkit to escalate further after Trump imposed sanctions on Russia on Wednesday for the first time since returning to office in January.

Trump has positioned himself as a global peacemaker, but has admitted that trying to end Russia's more-than-three-year war in neighbouring Ukraine has proven harder than he had anticipated.

His meeting with Putin in Alaska in August failed to make progress. Trump told reporters in Doha on Saturday that he would not meet with Putin again unless a peace deal appeared likely. "I'm not going to be wasting my time," Trump said.

European allies — buffeted by Trump's swings between accommodation and anger toward Putin — hope he will continue to increase pressure on Moscow.

One senior US official told Reuters that he would like to see European nations make the next big Russia move, which could be additional sanctions or tariffs. A separate source with knowledge of internal administration dynamics said Trump was likely to hit pause for a few weeks and gauge Russia's reaction to Wednesday's sanctions announcement.

Those sanctions took aim at oil companies Lukoil and Rosneft. The moves spiked oil prices by more than $2 and sent major Chinese and Indian buyers of Russian crude looking for alternatives.

Trump said on Saturday that when he meets with President Xi Jinping on Thursday, China's purchases of Russian oil may be discussed. But China is cutting back "very substantially" on Russian oil and "India is cutting back completely," Trump told reporters.

Some of the additional sanctions prepared by the United States target Russia's banking sector and the infrastructure used to get oil to market, said a US official and another person familiar with the matter.