ABOARD AIR FORCE ONE (Reuters) -U.S. President Donald Trump reiterated on Sunday that Indian Prime Minister Narendra Modi told him India will stop buying Russian oil, while warning that New Delhi would continue paying "massive" tariffs if it did not do so.

"I spoke with Prime Minister Modi of India, and he said he's not going to be doing the Russian oil thing," Trump told reporters aboard Air Force One.

Asked about India's assertion that it was not aware of any conversation between Modi and Trump, Trump replied: "But if they want to say that, then they'll just continue to pay massive tariffs, and they don't want to do that."

Russian oil has been one of the main irritants for Trump in prolonged trade talks with India - half of his 50% tariffs on Indian goods are in retaliation for those purchases. The U.S. government has said petroleum revenue funds Russia's war in Ukraine.

India has become the biggest buyer of seaborne Russian oil sold at a discount after Western nations shunned purchases and imposed sanctions on Moscow for its 2022 invasion of Ukraine.

Trump on Wednesday said Modi had assured him that day that India would stop its Russian oil purchases. India's foreign ministry said it was not aware of any telephone conversation between the leaders that day, but said that New Delhi's main concern was to "safeguard the interests of the Indian consumer."

A White House official said on Thursday that India has halved its purchases of Russian oil, but Indian sources said no immediate reduction had been seen.

The sources said Indian refiners already placed orders for November loading, including some slated for December arrival, so any cut may start showing up in December or January import numbers.

India's imports of Russian oil are set to rise about 20% this month to 1.9 million barrels per day, according to estimates from commodities data firm Kpler, as Russia ramps up exports after Ukrainian drones hit its refineries.