President Volodymyr Zelensky of Ukraine on Thursday redoubled his call for an independent tribunal to investigate and prosecute Russian war crimes, using a speech in The Hague to demand accountability and invoking the trials of Nazis in Nuremberg after World War II.
“Impunity is the key that opens the door to aggression,” Mr. Zelensky said in 15-minute remarks, which he delivered in English. “If you look at any war, any war of aggression in the history, they all have one thing in common: The perpetrators of the war didn’t believe they would have to stand to answer for what they did.”
Though the speech — in the city that houses the International Criminal Court and is a symbol of international law and justice — was not the first time Mr. Zelensky has called for such a tribunal, his remarks came as international backing for such an initiative appears to be growing. Allies of Ukraine, including the United States and other leaders of Group of 7 nations, have reaffirmed their support for at least exploring such a tribunal.
Earlier on Thursday, Mr. Zelensky visited the I.C.C., which was established in 2002 to deal with war crimes cases. In March, the court issued an arrest warrant for President Vladimir V. Putin and another Russian official on war crimes charges, accusing the Russian president of bearing criminal responsibility for the abduction and deportation of Ukrainian children.
“We all want to see different Vladimir in The Hague,” Mr. Zelensky said in his speech, referring to Mr. Putin, drawing laughter.
The special tribunal he has called for would run in parallel to cases pursued by the I.C.C. against Mr. Putin and others. The crime of aggression, the legal doctrine that would most directly hold Russian leaders to account for the invasion of Ukraine, cannot be pursued against Russia by the I.C.C. because it lacks jurisdiction.
First recognized as an international crime in the Nuremberg Trials of prominent Nazis, a crime of aggression is defined as being perpetrated by a leader — “a person in a position effectively to exercise control over or to direct the political or military action of a state” — by engaging in “the use of armed force by a state against the sovereignty, territorial integrity or political independence of another state” in violation of the United Nations Charter.
Mr. Zelensky said that “true justice” could be achieved only if leaders “make bold decisions that will correct the shortcomings of those norms that unfortunately exist in international law.”
Adding to the symbolism of the address, Mr. Zelensky, who carefully tailors his speeches to foreign audiences, spoke on the date that the Dutch people remember victims of war. And he called for a moment of silence for what he called victims of Russia after mentioning the crash in 2014 of a Malaysia Airlines jet over eastern Ukraine in which 298 people, most of them Dutch, lost their lives. Last year, a Dutch court found that an antiaircraft missile system provided to Russian-backed separatist forces brought down the plane, convicting three men with ties to the Russian security services and sentencing them to life in prison.
Mr. Zelensky’s trip to the Netherlands — where he also met Willem-Alexander, the Dutch king, and spoke to lawmakers and the Dutch and Belgian prime ministers — was not announced beforehand. It comes amid a tour by the Ukrainian leader of European countries that have contributed to his nation’s defense; he visited Finland on Wednesday, and next week, he is scheduled to make a two-day trip to Germany.
During a news conference with Prime Ministers Mark Rutte of the Netherlands and Alexander De Croo of Belgium, Mr. Zelensky called for additional weapons and asked for Ukrainian pilots to immediately begin training on Western-made F-16 fighter jets in anticipation of an eventual delivery.
After sending Western-made battle tanks to Ukraine this year, the fighter jets are one of the last major weapon systems that Western allies are reluctant to share, citing concerns about escalating the conflict and the significant training Ukrainian pilots would need to effectively fly them in combat.
Mr. Rutte noted that there was strong support in the Dutch Parliament to deliver the planes as part of a Western consortium of donor countries. “On the F-16s, no taboo,” he said.
Mr. Zelensky also discussed the counteroffensive that Ukraine is widely expected to undertake soon. “We are doing our best,” he said, adding: “Not only our military, but also society, our factories, our entrepreneurs — everyone is thinking about how to strengthen our army every day.”
The Dutch foreign minister, Wopke Hoekstra, said on Thursday that the Dutch government was prepared to host a tribunal for Russian war crimes, saying: “We will do everything in our power to ensure that Russia is being held to account.”
In his speech, Mr. Zelensky said that in April alone, Ukrainian prosecutors counted 6,139 Russian war crimes, including the deaths of 207 people, including 11 children. The Kremlin has denied accusations of war crimes, but international and Ukrainian investigators have gathered powerful evidence of an array of atrocities since the invasion’s early days.
Claire Moses contributed reporting.