A cap on the price of Russian oil will restrict Russia's revenues for the "illegal war in Ukraine," the US says.
The cap, approved by Western allies on Friday, is aimed at stopping countries paying more than $60 (£48) for a barrel of seaborne Russian crude oil.
The measure - due to come into force on Monday - intensifies Western pressure on Russia over the invasion.
Ukraine said the Western-proposed cap should be halved. Russia said it would not supply to countries enforcing it.
The price cap was put forward in September by the G7 group of industrialised nations (the US, Canada, the UK, France, Germany, Italy, Japan and the EU) in a bid to hit Moscow's ability to finance the war in Ukraine.
In a joint statement, the G7, the European Union and Australia said the decision was taken to "prevent Russia from profiting from its war of aggression against Ukraine".
