The $20bn will give the country “a critical infusion of support” as it defends itself “against an unprovoked war of aggression,” Yellen said in a statement on Tuesday.
It follows months of discussion among the US and its allies, including the EU, on how to use the approximately $325bn (£276bn) worth of assets that were frozen since Russia’s full-scale invasion of Ukraine began in 2022.
In October, the G7 agreed to use the interest generated by the assets – around $3bn (£2.4bn) a year – to fund $50bn in credit over 30 years. Payments were expected to start by the end of the year.
The EU has committed more than €18bn (£15bn) funded in the same way.
The $50bn is intended to ensure Ukraine has “the resources it needs to sustain emergency services, hospitals, and other foundations of its brave resistance,” Yellen said.
It comes at a critical juncture for Ukrainian President Volodymyr Zelensky’s forces, who have been ceding territory recently.
Moscow has been retaking ground in eastern Ukraine and in Russia’s Kursk – which Ukrainian forces launched an offensive in over the summer – while Ukrainian troops have painted a dismal picture of the war’s frontlines.