President Donald Trump has said Indian Prime Minister Narendra Modi has agreed to stop buying Russian oil, as the US seeks to tighten financial thumbscrews on the Kremlin as part of efforts to end the war in Ukraine.

Trump told reporters he had received assurances from Modi that India would halt its purchases "within a short period of time", which he called "a big stop".

A spokeswoman for the Indian embassy in Washington DC would not comment. The US president has sought to leverage India's purchases of Russian oil in his trade war, but New Delhi has resisted, creating a diplomatic rift.

Oil and gas are Russia's biggest exports, and Moscow's biggest customers include China, India and Turkey.

"Now I've got to get China to do the same thing," Trump said in the Oval Office on Wednesday.

His administration is also pushing Beijing, and other trading partners, to stop buying oil from Russia, part of a broader push to cut off Moscow's energy funding.

India cannot "immediately" halt oil shipments, Trump said, adding that the shift will be "a little bit of a process, but the process is going to be over with soon".

The Trump administration has imposed 50% tariffs on goods from India, levies that Trump has characterised as punishment against New Delhi for buying Russian oil and weapons.

The tariffs – which took effect in August and are among the highest in the world – include a 25% penalty for transactions with Russia that are a key source of funds for its war in Ukraine.

Modi has for months stood his ground, arguing that India is neutral in the Russia-Ukraine war despite his country's ties with Russian leader Vladimir Putin.

Indian officials have called the Trump administration's accusations that Delhi profits from Russia's war in Ukraine a double standard, citing ongoing trade with Russia in the US and Europe.

India relies on Russian crude oil, which Delhi has continued to buy at a discount, to support its economy - the fifth largest in the world.

The dispute over Russian oil has strained the relationship between Trump and Modi, although the US president on Wednesday praised the Indian leader as a "great man".

Modi said last week that he spoke with Trump and that they "reviewed good progress achieved in trade negotiations".