Every sovereign country has the right to freeze foreign assets (not to seize them) belonging to foreign citizens (not international companies or foundations and trusts) inside his borders without international courts and arbitration. It has to be owned by foreign individuals. That what being sovereign is all about. You can go to international arbitration to release the assets.
About US position, US will not do a darn thing. They are both trying to save face and look tough just like KGB said. It is the movie Back to the Past VI, with the same plot but different leading actors. Just as usual the extras are suffering.