Ukraine's President Volodymyr Zelensky has condemned a US decision to extend the period during which Russia is allowed to sell oil despite Western sanctions.
The move means countries can purchase Russian oil and petroleum products already loaded on vessels at sea until 16 May.
The US argues that the waiver is meant to ease the energy supply crunch sparked by the US-Israel war with Iran.
But in his remarks on Sunday, Zelensky said "every dollar paid for Russian oil is money for the war" in Ukraine. Widespread sanctions have been in place against Russia since President Vladimir Putin launched his full-scale invasion of its neighbour in February 2022.
The devastating US and Israel attacks against Iran have prompted it to retaliate not only against Israel and US military bases in the Gulf, but also against energy fatalities and other civilian sites across Arab allies of the US in the region.
Additionally, Iran has virtually shut the Strait of Hormuz - the narrow passage where some 20% of the world's oil and liquefied natural gas (LNG) is usually transported through.
This has led to turmoil in energy markets, with fears that a world recession may ensue if it is not reopened soon.
The US move to ease Russian sanctions on 13 March was widely condemned by Zelensky as well as his European allies.
Extending the waiver on Friday, the US said it wanted "to ensure oil is available to those who need it" as negotiations to end the war "accelerate".
The Ukrainian leader said Russia had more than 110 tankers from its "shadow fleet" - vessels with obscured ownership designed to help it bypass sanctions - with "over 12 million tons" of oil.
Their sale, he added, would bring $10bn (£7.4bn) to Moscow's coffers as "a resource that is directly converted into new strikes against Ukraine".
The Ukrainian leader did not explain what those figures were based on.
But he added that just over the past week, Russia had launched "over 2,360 attack drones, more than 1,320 guided aerial bombs, and nearly 60 missiles of various types at our cities and communities".
That included the deadliest attack against Ukraine in months on 15 April during which more than 700 drones and missiles were used in multiple waves in one night, killing at least 18 people.
Ukraine has also attacked Russia, particularly focusing on energy facilities.
However, despite ongoing attacks, a stalemate has been reached in the war in Ukraine, with Russia in control of about 20% of Ukrainian territory.
Efforts led by the US to end the war have been put on hold as a result of the war in Iran.
