Russia says it will not accept a cap on prices for its oil exports approved by Western allies.
The cap, approved 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.
But Kremlin spokesman Dmitry Peskov said that Moscow had prepared for the move and was assessing its options.
“We will not accept this ceiling,” he said.
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.
The White House described the deal as “welcome news”, saying a price cap will help limit Putin’s ability to fund the Kremlin’s “war machine”.
UK Chancellor Jeremy Hunt said the UK would not waver in its support for Ukraine and would continue to look for new ways to “clamp down on Putin’s funding streams”.
Though the measures will most certainly be felt by Russia, the blow will be partially softened by its move to sell its oil to other markets such as India and China – which are currently the largest single buyers of Russian crude oil.