Russia has protested to the Belgian ambassador over the seizure of Russian state assets in Belgium – a move triggered by a court ruling over the now-defunct Yukos oil firm.
The ambassador was told that the asset seizure was “an openly hostile act” that “crudely violates the recognised norms of international law”.
Last year a court told Russia to pay Yukos shareholders $50bn (£32bn) in compensation, after Yukos’s break-up.
A Russian state firm took over Yukos.
In July 2014, an international arbitration court in The Hague said Russian officials had manipulated the legal system to bankrupt Yukos, and jail its boss, the oligarch Mikhail Khodorkovsky.
On Friday, President Vladimir Putin said Russia did not recognise the court’s authority.
Responding to the asset seizure, he said Russia would “defend our interests by the route of justice”.
France has also seized Russian state accounts in about 40 banks, along with eight or nine buildings, AFP news agency reports.
And a legal application has also been filed to seize Russian state assets in the UK and US, a lawyer acting for Yukos shareholders told the BBC.
Lawyer Tim Osborne is the director of GML, a Gibraltar-registered holding company representing the shareholders.
“The Russian state has made no effort to pay or engage with us – all of its statements and actions suggest it has no regard for international law or the rule of law,” he told the BBC.
He said asset seizure was slower in the UK and US – under their Common Law system – than in France and Belgium.
“I think it’ll take years to seize assets here because Russia will use tactics to delay,” he said.
The targeted assets are mostly bank accounts and real estate, but “at some stage we’ll look at state-owned companies too,” he added.
In a statement on Facebook, Mr Khodorkovsky, who spent 10 years in detention in Russia, expressed joy at the asset seizures.
“I am not a beneficiary in this process as the partners redeemed my share back in 2004. But this does not prevent me from sincerely rejoicing, as a Russian citizen, at what is happening now.
“This is a symbolic moment for our country,” he said, calling it “a signal that theft will not escape punishment, no matter how all-powerful the thief was”.
A Russian foreign ministry statement (in Russian) said Russia demanded that Belgium reverse its asset seizure.
If no such action was taken, Russia warned, it would consider “appropriate reciprocal measures” against the Belgian embassy and unnamed Belgian officials.
Earlier, Russia’s Economic Development Minister Alexei Ulyukayev ruled out any compensation for Yukos shareholders. Russia is appealing against the court ruling of last July.
Mr Osborne said GML was waiting for the court in The Hague to announce an appeal hearing. But he called the Russian appeal “frivolous”.
The asset seizures in Belgium and France also affect Russian media, including Tass news agency and state broadcaster VGTRK, Russian media report.
Yukos shareholders also sued the Russian state at the European Court of Human Rights. In a ruling last July the ECHR ordered Russia to pay them about $2.5bn. Russia has not paid them yet.
Yukos was disbanded in 2007 after filing for bankruptcy in 2006. Mr Khodorkovsky, once Russia’s richest man, now lives abroad. He was pardoned and released from jail in Siberia in December 2013.