Lawmakers accused the Pentagon on Thursday of effectively undermining war crimes prosecution of Russia by blocking the sharing of U.S. military intelligence with the International Criminal Court at the Hague.

U.S. Senator Dick Durbin, a Democrat, said at Senate hearing that he had been told by the ICC’s chief prosecutor, Karim Khan, that the U.S. State Department and Justice Department were both cooperating. But the Defense Department, under the leadership of Defense Secretary Lloyd Austin, was refusing, Durbin added.

“Why are you reluctant to share the evidence that we have gathered in the United States through the Department of Defense for those who are holding Vladimir Putin accountable for his war crimes?” Durbin asked Austin, referring to the Russian president.

The ICC, a permanent war crimes tribunal, in March issued an arrest warrant for Putin for suspected deportation of children from Ukraine, which would be a war crime.

“Why we would hold back evidence against this war criminal Vladimir Putin and the terrible things he’s doing, I don’t understand at all,” Durbin said.

Austin, a retired Army general who is rarely expansive in his answers to the public, did not deliver a detailed defense of his position at the hearing, where Durbin and another lawmaker urged him to follow a law passed last year allowing international cooperation to hold Russia accountable.

But Austin alluded to the U.S. military’s longstanding concerns that any cooperation with the court could open the way for politicized prosecution of American troops deployed overseas.

“I will always prioritize the protection of U.S. military personnel,” Austin said.

When pressed, Austin responded: “We support the goal of holding hold them (the Russians) accountable. But again, I do have concerns about reciprocity going forward.”

Senator Lindsay Graham, a Republican, suggested that prosecuting Putin and those Russians responsible for war crimes would have a U.S. national security benefit. Graham also pressed Austin to cooperate and to abide by a law written by Congress on the matter.

“Mr. Khan says we have a lot of valuable information that could accelerate his prosecution not only of Putin but of others,” Graham said.

At a hearing last month, Graham praised the Justice Department for working with its Ukrainian counterpart to help pursue war crimes prosecutions against Russia and bashed the Defense Department for hindering such efforts. At the time, Deputy Attorney General Lisa Monaco declined to comment on internal discussions.

A State Department spokesperson said the United States supports a “a range of international investigations and inquiries into war crimes and atrocities in Ukraine.” The spokesperson said this includes those conducted by the ICC’s prosecutor.

Ukrainian President Volodymyr Zelenskiy made a surprise visit to The Hague a week ago, calling for a new international tribunal to hold Putin accountable for the invasion of Ukraine launched in February 2022.

Russia is not a member of the ICC and rejects its jurisdiction. It denies committing atrocities during its conflict with Ukraine, which it terms a “special operation” to “demilitarize” its neighbor.