President Donald Trump announced an additional 25% tariff on India as punishment for importing Russian oil, according to a document posted on the White House website — an escalation of his trade battle with New Delhi and his first use of so-called secondary sanctions on countries the US says are fueling Moscow’s war machine.

"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.