Ukrainian officials are growing wary over delays in finalizing a deal that would unlock $50 billion in support by harnessing the profits of frozen Russian central bank assets, according to people familiar with the matter.

Those funds are intended to flow to Kyiv by the end of the year, according to a Group of Seven agreement in June that foresaw a loan syndicate to be paid back by profits generated over time by some $280 billion in frozen Russian funds.

But the implementation of the plan has been snarled by demands made by the U.S. and the risk of Hungary slowing down any EU-wide decision on support for Ukraine or sanctions against Russia, according to the people, who spoke on condition of anonymity as talks take place behind closed doors.