Defense Secretary Lloyd Austin met with the defense leaders of more than 40 countries on Monday morning to discuss Russia’s war in Ukraine.

This is the second meeting of the Ukraine Defense Contact Group, which convened in late April at Ramstein Air Base in Germany. Ukrainian Defense Minister Oleksii Reznikov participated in the virtual meeting to represent his country.

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Monday’s meeting of defense leaders included representatives from 44 nations, Austin said while addressing reporters before the meeting commenced. Several countries participated in Monday’s event that were not at the April 26 meeting, including Austria, Bosnia-Herzegovina, Colombia, Ireland, and Kosovo.

“We’ve watched these efforts make a real difference in real time. Now, as Ukraine's fight continues, our efforts must intensify, and we must all plan for the challenges ahead,” Austin said in remarks to reporters ahead of the meeting, adding that he was “very encouraged” by the progress the United States and other allies have made since the first.

"Several countries announced new donations of critically needed artillery systems and ammunition, including Italy, Greece, Norway, and Poland," the secretary announced in a press conference after the countries met. "Everyone here understands the stakes of this war, and they stretch far beyond Europe.

Austin called Russian aggression "a challenge to free people everywhere."

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Following the meeting at Ramstein, Austin left open the possibility of Ukraine joining NATO.

"I think that NATO will always stand by its principles of maintaining an open door, so I don't want to speculate on what could come," he said. "I do believe that, you know, in the future, if the possibility exists, I think Ukraine will seek to once again apply to become a member of NATO. But again, that's probably a bit down the road, and speculation at this point is not very helpful."

The secretary also announced that the group would meet next month in Brussels.