US President Donald Trump on Wednesday signed an order to impose an additional 25 per cent tariff on Indian goods over New Delhi's continued purchase of Russian oil, a key revenue source for Moscow's war in Ukraine.

The tariff, set to take effect in three weeks, comes on top of a separate 25 percent duty entering into force on Thursday, according to the text of the executive order released by the White House.

The order also threatens potential penalties on other countries deemed to be "directly or indirectly importing Russian Federation oil."