As the International Court of Justice in The Hague works to determine if it has jurisdiction over Ukraine's case against Russia, an international tribunal has been set up in the same Dutch city to try Russian President Vladimir Putin and his circle for the alleged crime of aggression.

The International Centre for the Prosecution of the Crime of Aggression Against Ukraine is based at the European Union's judicial office Eurojust.

"Of course, that person (Putin) should be tried for aggression against Ukraine, because this is his crime, because he engineered this war. Back in 2014, he was part and parcel of this aggression, and he still is," Anton Korynevych, Ukraine's top lawyer at the ICJ, said.

Korynevych, 37, said the tribunal is not just about Putin but will also prosecute 20 Russian political and military leaders.

A group of prosecutors from Ukraine, the EU, the United States and the ICJ is already gathering evidence including photos and communications intercepts.

"I do not believe this is an academic exercise. And I do believe that the world in general needs a legal reaction to this situation," Korynevych said, referring to Russia's invasion of his country.

"It is important for us to say that accountability and justice is taking place and… for us to show that it's not only Ukraine that says that Russia violated international law, but that also international courts and tribunals say this."

While the top priority for Ukraine was of course victory on the battlefield, Korynevych feels that grappling with his opponents in the courtroom is his way of contributing to the war effort.

Meanwhile, the Ukrainian military on Thursday said that Russia had launched a "massive" drone attack overnight and that it had destroyed 31 out of the 39 aircraft.

Russian UAVs were intercepted over Black Sea coastal regions and further inland, Nataliya Gumenyuk, spokesperson for the Ukrainian southern military command, said.