Belgian Prime Minister Bart De Wever has outlined three demands for the use of Russian immobilised assets to provide a €140 billion loan to Ukraine, adding that he would oppose the measure until he secures guarantees.
Mr De Wever, whose country is home to chief asset holder Euroclear, said he did not see the legal basis for such a decision, adding that immobilised assets had not even been touched in such a deflagration as World War II.
He told reporters - before a European Union summit in Brussel on the issue - that there needs to be full mutualisation of the risk of claims and guarantees that, if the money has to be paid back, then all member states will contribute.
Mr De Wever also said that every country that has mobilised assets should move at the same pace.
"We are the only ones, Euroclear is the only financial institution that offers the windfall profits to Ukraine.
"We know that there are vast amounts of Russian money in other countries who have always been silent about this," he said.
"If these three demands, which I think are quite reasonable, are met then we can go forward.
"If not, I will do everything in my power at the European level, also at the national level, politically and legally to stop this decision."
At the summit, leaders are expected to develop a proposal to use frozen Russian assets for the Ukraine loan.
European Council President António Costa said: "Today we will take the political decision to ensure Ukraine's financial needs for 2026 and 2027.
"The technicality of the solutions, we continue to work on with the European Commission, but the most important is the political decision."
Ukraine's President Volodymyr Zelensky is attending the summit.
He was welcomed to Brussels by Mr Costa who addressed him as a "future member of the European Union".
Taoiseach Micheál Martin said that Ireland supports the EU's plan to fund Ukraine.
He said there would be no implications for neutrality if Ireland acts as a co-guarantor for the loan.
Mr Martin was speaking on arrival in Brussels.
EU approves 19th package of sanctions against Russia
EU countries have formally adopted the 19th package of sanctions against Russia over its invasion of Ukraine.
They include a ban on liquefied natural gas (LNG) imports, said Denmark, which holds the rotating presidency of the European Council.
All but one of the member states agreed on the final text last week. Slovakia held out until its demands were met.
Its Prime Minister Fico wanted assurances from the European Commission on high energy prices and aligning climate targets with the needs of carmakers and heavy industry.
A Slovak diplomat said the demands were met in new clauses added to the final communique for this week's summit in Brussels.
The LNG sanction will take effect in two stages - short-term contracts will end after six months and long-term contracts from 1 January 2027.
The full ban comes a year earlier than the commission's proposed roadmap to end the bloc's reliance on Russian fossil fuels.
The new package also adds new travel restrictions on Russian diplomats and lists another 117 vessels from Moscow's shadow fleet, mostly tankers, bringing the total to 558.
It also include banks in Kazakhstan and Belarus, the presidency said.
EU diplomatic sources said that four entities linked to China's oil industry will be listed but the names will not be made public until the official adoption.
These include two oil refineries, a trading company and an entity which helps in the circumvention in oil and other sectors.
President Zelenskiy said the latest sanctions were "very important".
He added that a ceasefire was possible. However, he said that more pressure would have to be put on Russia to make it happen and ruled out making any territorial concessions to Moscow.
