US President Donald Trump again on Tuesday said he would increase the tariff charged on imports from India from the current rate of 25 per cent "very substantially" over the next 24 hours, given India's continued purchases of Russian oil.

"They're fueling the war machine, and if they're going to do that, then I'm not going to be happy," Trump told CNBC in an interview, adding that the main sticking point with India was that its tariffs were too high.

"India has not been a good trading partner, because they do a lot of business with us, but we don't do business with them. So we settled on 25 per cent (tariff), but I think I'm going to raise that very substantially over the next 24 hours, because they're buying Russian oil," he added.

When asked about the trade deal with India that seemed imminent, Trump said the “sticking point” with India is that its tariffs are too high.

“Now I will say this, India went from the highest tariffs ever, they will give us zero tariffs….But that's not good enough, because of what they're doing with oil.”

Russia on Tuesday accused the United States of exerting “illegal” trade pressure on India after Trump renewed his threat to raise tariffs on New Delhi over its purchases of Russian oil.

"We hear many statements that are in fact threats, attempts to force countries to cut trade relations with Russia. We do not consider such statements to be legal," Kremlin spokesman Dmitry Peskov told reporters.

"We believe that sovereign countries should have and do have the right to choose their own trading partners, partners for trade and economic cooperation, and to choose for themselves the forms of trade and economic cooperation that are in the interests of a particular country," he added.

In a social media post on Monday, Trump wrote, "India is not only buying massive amounts of Russian Oil, they are then, for much of the Oil purchased, selling it on the Open Market for big profits. They don't care how many people in Ukraine are being killed by the Russian War Machine."

"Because of this, I will be substantially raising the Tariff paid by India to the USA," he added.

A spokesperson for India's foreign ministry said in response that India will "take all necessary measures to safeguard its national interests and economic security."

"The targeting of India is unjustified and unreasonable," the spokesperson added.

Trump has said that from Friday he will impose new sanctions on Russia as well as on countries that buy its energy exports, unless Moscow takes steps to end its 3-1/2 year war with Ukraine. Russian President Vladimir Putin has shown no public sign of altering his stance despite the deadline.

Over the weekend, two Indian government sources told Reuters that India will keep purchasing oil from Russia despite Trump's threats.

India has faced pressure from the West to distance itself from Moscow since Russia invaded Ukraine in early 2022. New Delhi has resisted, citing its longstanding ties with Russia and economic needs.

On August 1, Trump signed an Executive Order titled 'Further Modifying The Reciprocal Tariff Rates’, raising tariffs for over five dozen countries, including a steep 25 per cent for India.

The executive order, however, did not mention the “penalty” that Trump had said India will have to pay because of its purchases of Russian military equipment and energy.

White House Deputy Chief of Staff Stephen Miller, in an interview to Fox News Sunday, stated that President Trump has said very clearly that “it is not acceptable for India to continue financing" the Ukraine war by purchasing oil from Russia.

Last week, Trump mounted a sharp attack on India and Russia for their close ties and said the two countries can take their "dead economies down together", a remark which prompted New Delhi to say that India is the world's fastest-growing major economy.

Trump had earlier announced a 25 per cent tariff on imports of Indian goods along with an unspecified "penalty" for buying "vast majority" of Russian military equipment and crude oil.

Declaring that the US has a massive trade deficit with India, Trump had said that while “India is our friend, we have, over the years, done relatively little business with them because their tariffs are far too high, among the highest in the world, and they have the most strenuous and obnoxious non-monetary Trade Barriers of any country.

"Also, they have always bought a vast majority of their military equipment from Russia, and are Russia's largest buyer of energy, along with China, at a time when everyone wants Russia to stop the killing in Ukraine — All things not good!” Trump had said.