A White House official has described Russia's ongoing war with Ukraine as Indian Prime Minister Narendra "Modi's war", stepping up pressure on Delhi to stop buying oil from Moscow.

US Trade Adviser Peter Navarro's comments came hours after US tariffs of 50% on Indian goods kicked in on Wednesday.

The tariffs, among the highest in the world, include a 25% penalty for purchase of weapons and oil from Russia which, the US claims, is a key source of funds for its war in Ukraine.

India has called the tariffs unfair and says it will not scale back purchases, insisting it will seek the "best deal" on oil to safeguard the interests of its 1.4 billion people.

Russia, which supplied less than 2% of India's crude before it invaded Ukraine in February 2022, now accounts for 35-40% of Delhi's oil imports, making it the largest source.