WARSAW, Poland — Polish Prime Minister Donald Tusk pledged Thursday to push ahead with a “great modernization program” for his country’s military, a day after Russian drones crossed into Poland and forced the NATO alliance to confront a potential threat in its airspace for the first time.

European officials described Wednesday’s incursion, which occurred during a wave of unrelenting Russian strikes on Ukraine, as a deliberate provocation. It deepened longstanding fears that the three-year war between Poland’s neighbors could precipitate a wider conflict. U.S.-led efforts to steer Moscow and Kyiv toward a peace settlement have so far failed to get traction.

The Polish Air Navigation Agency announced Thursday morning that Poland was introducing air traffic restrictions in the eastern part of the country. It said the step was taken at the request of the Polish army for national security reasons but did not elaborate.

Poland said some of the drones that entered its airspace Wednesday came from Belarus, where Russian and local troops have begun gathering for war games scheduled to start Friday. Poland is closing its border with Belarus at midnight Thursday, a planned move also associated with the military exercises.

Tusk addressed Polish troops at an air base in the central city of Lask, praising their quick action and that of NATO allied forces from the Netherlands that responded to the multiple Russian drone incursions.

Poland expects to receive its first F-35 fighter jets from the United States next year, he said. It will be the first delivery of some of the 32 aircraft expected by 2030 as part of a support package finalized five years ago, Tusk said.

The jets are aimed at significantly strengthening Polish security and its NATO defense capabilities against regional threats.

“We will do everything to ensure that our allied obligations, which are so important from our point of view today, are fulfilled by our allies,” Tusk said

“We hope that the Americans will meet the deadlines. We would like the first batch of the F-35s to reach you in May, and so that we can speak of our air power with increasing confidence from month to month, and from year to year. And that Poland is truly safe from the sky.”

U.S. President Donald Trump on Wednesday offered an ambiguous initial response to Russia’s drone incursion. “What’s with Russia violating Poland’s airspace with drones? Here we go!” Trump posted on social media.

Trump told Polish President Karol Nawrocki in the White House last week that the U.S. will maintain a robust military presence.

Several European leaders said they believed the incursion amounted to an intentional expansion of Russia’s assault against Ukraine.

“Russia’s war is escalating, not ending,” European Union foreign policy chief Kaja Kallas told reporters in Brussels on Wednesday. “What (Russian President Vladimir) Putin wants to do is to test us. What happened in Poland is a game changer,” she said, adding that it should result in stronger sanctions.

Polish airspace has been violated many times since Russia’s full-scale invasion of Ukraine in 2022, but never on this scale in Poland or anywhere else in NATO territory.

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