The finance ministers of the G7 agreed on Friday to move forward with a plan to put a price cap on purchases of Russian oil and petroleum products over the country's invasion of Ukraine.

Why it matters: The ministers said the cap, proposed by G7 leaders back in June, is aimed at limiting the invasion's effect on global energy prices while preventing the Kremlin from further profiting from its oil exports while damaging its ability to fund its war against Ukraine.

What they're saying: "We remain steadfast in our support for and solidarity with Ukraine. We will continue to stand with Ukraine for as long as it takes," the finance ministers said.

U.S. Treasury Secretary Janet Yellen said in a statement Friday that the agreement is "a critical step forward in achieving our dual goals of putting downward pressure on global energy prices while denying Putin revenue to fund his brutal war in Ukraine."

The other side: Officials in Russia, a key oil exporter, threatened on Thursday — and again today — to withhold sales to countries that take part in the capping plan.

The big picture: The ministers said they hope to time the implementation of the price cap with the European Union's sixth sanctions package against Russia, which in part banned imports of Russian seaborne crude oil and petroleum products.

What's next: Crafting the specifics. The document invites input on the design, and says the initial cap will be "at a level based on a range of technical inputs."

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