Yellen spoke at the Brussels Economic Forum hosted in the Belgian capital on Tuesday, bringing together key policy-makers.
Ukraine needs a new Marshall Plan, according to US Treasury chief, as Western nations grapple with the rising economic volatility caused by Russia's war in Ukraine.
Speaking at the Brussels Economic Forum on Tuesday, Secretary of the Treasury Janet Yellen voiced concern that costs for the conflict keep mounting despite funding efforts from Western allies.
Yellen was in the Belgian capital ahead of a meeting of finance ministers for the Group of 7 (G7) leading economies in Germany.
"What's clear is that the bilateral and multilateral support announced so far will not be sufficient to address Ukraine's needs, even in the short term," Yellen said on Tuesday.
"And I sincerely ask all our partners to join us in increasing their financial support to Ukraine."
War raises concerns of slowing down green transition
The Marshall Plan was a financing project backed by the US following World War II designed to help rebuild European economies.
And it is now that the war in Ukraine has led to worries in the EU that major policy objectives like the Green Deal could now move to the back burner and slow the transition to a climate-neutral economy.
But the European Commission sees the current situation rather as an opportunity to accelerate the transition process.
"The war in Ukraine is not forcing us to change our climate targets, climate neutrality by 2050, 55% emission reduction targets by 2030," Valdis Dombrovskis, Executive Vice President of the European Commission told Euronews.
"If anything, it is making this transition more urgent because we have taken strategic decisions quickly moving away from Russian fossil fuels."
According to Luc Triangle, secretary-general of IndustriALL trade union, accelerating the climate transition is a noble goal, but not without sufficient social measures.
"The Green Deal has to be first and foremost a social deal, no one should be left behind, no region should be left behind," Triangle said.
"But it should go beyond slogans, there need to be concrete deliverables on the social dimension, and for the moment, we see recommendations, we see guidelines, but we don't see enough social action."