Ukrainian President Volodymyr Zelenskyy's chief of staff said on Tuesday that the postponement of U.S. assistance for Kyiv being debated in Congress would create a "big risk" of Ukraine losing the war with Russia.

The remarks by Andriy Yermak were some of the frankest yet from a senior Ukrainian official as uncertainty swirls over the future of vital U.S and European Union assistance packages as Ukraine's war with Russia rages on.

If the aid is postponed, "it gives the big risk that we can be in the same position to which we're located now," he said.