BRUSSELS — Defense Secretary Pete Hegseth on Wednesday warned the U.S. will “impose costs on Russia” if it does not seek to end the Ukraine war, his strongest criticism yet of Moscow and a signal of the administration’s increasing support for Kyiv.

Hegseth’s comments, which came during a meeting focused on Ukraine at NATO headquarters, reflect the White House’s deepening frustration with Russian President Vladimir Putin ahead of a Friday meeting between President Donald Trump and Ukrainian President Volodymyr Zelenskyy.

“If there is no path to peace in the short term then the United States, along with our allies, will take steps necessary to impose costs on Russia for its continued aggression,” Hegseth said, without naming specifics.

His comments are an about-face from his first appearance at NATO headquarters in February, when he told allies the U.S. had other more pressing interests in the world and would likely turn away from Europe. The move unsettled some European nations, who feared the new administration would pull troops from the continent and back away from the NATO alliance.

Hegseth declined to attend the last several meetings of the Ukraine Defense Contact Group, the assembly he addressed Wednesday. At one point over the summer, he briefly stopped U.S. military aid for Kyiv.

His tone was a remarkable shift for an administration that earlier this year publicly berated Zelenskyy. Trump and Vice President JD Vance in February attacked the Ukrainian leader ina withering Oval Office exchangefor overplaying his hand.

By Wednesday’s NATO gathering, much of that checkered past seemed long forgotten, at least in public comments. The U.S. remains “clear-eyed about the fact that the most effective deterrents to Russian aggression are number one: a lethal, capable and European-led NATO, and number two: a combat credible Ukrainian military,” Hegseth said.

The recent chill with Moscow comes after months of overtures to the Russian leader by Trump and his advisers. Trump in August held a face-to-face meeting with Putin in Alaska, which startled Kyiv and many in Europe who feared he would listen to the Russian president’s version of the war.

While Trump talked up the meeting as a potential breakthrough, Putin followed up by launching the most brutal drone and missile attacks on Kyiv of the four-year war. They killed dozens of civilians.

Trump, who has grown frustrated with Putin’s increasing brutality and refusal to consider any sort of ceasefire, has held several phone calls and face-to-face meetings with Zelenskyy in recent months. He has pledged more U.S. support and even suggested on Sunday that he might send Tomahawk missiles to Ukraine so it could launch deep strikes into Russia.

The Friday meeting between the two leaders will include discussions about military aid and a proposed deal for Ukraine to share drone technology with the U.S.

Some ministers expressed relief about Hegseth’s comments. “He confirmed once again that the U.S. is a true ally and is committed to NATO and this is exactly what also President Trump said,” Estonian defense minister Hanno Pevkur said in an interview.

But some European leaders remain cautious, given the yo-yo aspect of the Trump administration’s policy on Ukraine. “I would read into that a kind of change of perspective and approach, but not more for the moment,” German Defense Minister Boris Pistorius told reporters when asked about Hegseth’s comments. “I can’t interpret, really, what he did mean.”

Hegseth also praised a new European effort to buy American weapons for Ukraine, which he said is vital to helping Kyiv defend itself. “European leaders are sending a clear message to Russia,” he said. “Now is the time to end this tragic war, stop the needless bloodshed, and come to the peace table.”

A NATO official, granted anonymity to speak about military operations, underscored the continuing American commitment to Ukraine.

The alliance has “seen no sign of reduced [intelligence] sharing from the U.S. side,” the person said, adding the U.S. has committed “to providing significant intelligence support for any potential security guarantees,” implemented by European countries in Ukraine.