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 amplified international tensions around Russia’s invasion of Ukraine and what the Kremlin’s future territorial ambitions might be.

European officials described Wednesday’s incursion, which occurred during a wave of recent unrelenting Russian strikes on Ukraine, as a deliberate provocation, forcing the NATO alliance to confront a potential threat in its airspace for the first time.

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 tra

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