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.