New Delhi, Dec. 19 -- A core question for European Union leaders discussing whether to use frozen Russian assets to help Ukraine is whether the idea is legally sound. But even if they approve the plan, Russia has limited options for challenging it in court.

The 27-nation bloc's leaders are set to decide on whether to use tens of billions of euros in frozen Russian Central Bank assets to underwrite a loan to meet Ukraine's military and financial needs over the next two years. The bulk of the assets are held in Belgium-based financial clearinghouse Euroclear.

Belgium said Thursday that it wants ironclad guarantees that it will be protected from retaliation - legal, financial or otherwise - and that's become a major stumbling block.

Russi...