According to this article, Mladic's conviction by International Criminal Tribunal for the former Yugoslavia (ICTY) in The Hague found widespread international support. However, this opinion is not shared by all leaders (my emphasis):

However, the Serb member of the Presidency of Bosnia and Herzegovina,
Mladen Ivanic, said the court had not shared justice among Serbs,
Croats and Bosniaks.

"The Hague Tribunal has brought distrust instead of trust, and instead
of reconciliation, it will lead to new political conflicts. The
verdict of General Mladic shows that they continue with a negative
attitude towards the Serbs and that the Hague Tribunal will remain
remembered for not sharing justice but politics," Ivanic said.

Ivanic accused political interference in this case. This made me wonder about how judicial independence is ensured in such cases.

According to Wikipedia, "Judicial Independence is vital and important to the idea of separation of powers". However, separation of powers seems to be a concept at the state level, not international level:

The separation of powers, often imprecisely and metonymically used
interchangeably with the trias politica principle, is a model for the
governance of a state.

Question: How is judicial independence ensured for International Tribunals? Theoretically, they operate at an international level and classic separation of powers (state level) does not directly apply to them.