"The key channel by which secondary tariffs on buyers of Russian energy could impact the global economy would be through the level of energy prices," says Kieran Tompkins from the consultancy Capital Economics. If the tariffs work, they will cut the flow of Russian oil and gas to global markets.

U.S. President Donald Trump said on Tuesday he would increase the tariff charged on imports from India from the current rate of 25% "very substantially" over the next 24 hours, in view of New Delhi's continued purchases of Russian oil.