The EU should confiscate and sell Russian assets it has seized and use the proceeds to rebuild war-scarred Ukraine, EU chief Charles Michel said in an interview published Thursday.

The suggestion echoes an idea already floated in the United States, and comes as EU and US task forces hunt down and grab yachts, mansions, bank accounts, helicopters and artworks owned by Russian oligarchs sanctioned by the West.

The EU said early last month it had frozen 30 billion euros ($32 billion) in assets linked to blacklisted Russian and Belarusian individuals. The question now is what to do with those assets.

"Personally, I am absolutely convinced that this is extremely important not only to freeze assets, but also to make possible to confiscate it, to make it available for the rebuilding of the country (Ukraine)," Michel, president of the European Council, told the Interfax-Ukraine news agency.

He was the first high-ranking EU official to propose the confiscation of oligarchs' assets, his spokesman confirmed to AFP.

Ukraine's government in April estimated the cost of rebuilding after the war to be at least $600 billion (565 billion euros).

The EU, US, Britain and Canada have been steadily expanding their lists of wealthy sanctioned Russians deemed to influence or profit from Moscow's invasion of its pro-Western neighbour.

Last week, US President Joe Biden proposed oligarchs' seized assets be "sold off" to "remedy the harm Russia caused and to help build Ukraine".

But the American Civil Liberties Union has warned any legislation in that sense could violate due-process protections, as the targeted oligarchs would have no recourse to challenge the confiscations.

Similar legal concerns dog EU moves along the same line, acknowledged Michel, a lawyer by training.

Confiscation of sanctioned individuals' assets "is not so simple" and would be "a difficult and long process," he said.

But he said he has tasked the European Council's legal service to come up with ways of making it work "in line with the principles of rule of law".