Before relenting, Budapest had threatened to allow billions of dollars to flow back to the Kremlin in a row over energy imports.

Sikorski believes that Budapest changed its mind after Trump called Russian dictator Vladimir Putin as an aggressor and threatened Moscow with sanctions if it did not engage in peace talks. It was the new US president's first clear position on Russia's war against Ukraine.

The European Union renewed on Monday its wide-ranging sanctions on Russia over the war in Ukraine, after Hungary stopped holding up the move in return for a declaration on energy security.