US President Donald Trump on Wednesday ordered an additional 25 percent 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."

Exemptions remain for items targeted by separate sector-specific duties such as steel and aluminum, and categories that could be hit like pharmaceuticals.

Trump has been ramping up pressure on India after signaling fresh sanctions on Moscow if it did not make progress by Friday towards a peace deal with Kyiv, as Russia's devastating invasion of its pro-western neighbor drags on.

India's national security adviser was in Moscow on Wednesday, media in New Delhi reported, coinciding with a visit by US envoy Steve Witkoff.

India's foreign ministry earlier said US pressure to stop it buying Russian oil was"unjustified and unreasonable" and that it would protect its interests.