Lithuania has closed its border with Belarus following repeated “constant violations” of its airspace by dozens of helium balloons, officials announced Monday.

Prime Minister Inga Ruginienė called the incidents a hybrid threat and warned that the armed forces would take “all necessary measures” to shoot down intruding balloons.

European Commission President Ursula von der Leyen described the incursions as provocations and expressed full EU solidarity with Lithuania.

The violations come amid heightened NATO vigilance after multiple airspace breaches by Russian drones and fighter jets in Poland, Romania, and Estonia, with NATO launching the “Eastern Sentry” mission to reinforce Eastern Europe, CNN has reported.

European leaders are using these incidents to pressure Moscow toward negotiations to end the war in Ukraine.