Poland will close its border with Belarus at midnight Thursday in response to Russia’s large-scale Zapad military exercises, Prime Minister Donald Tusk announced.

The drills, held every four years with Kremlin-allied Belarus, are designed to simulate conflict with NATO and this year feature tens of thousands of troops operating dangerously close to Poland and Lithuania.

Tusk described the maneuvers as “very aggressive” and said they coincide with an increase in provocations from both Russia and Belarus.

The exercises will include simulated use of Oreshnik nuclear-capable missile systems and will focus heavily on the Suwałki Gap, a strategic 70-kilometer NATO corridor between Belarus and Russia’s Kaliningrad exclave, Politico has reported.

Poland has previously restricted border access with Belarus, including closing checkpoints and halting asylum applications for migrants, accusing Minsk of weaponizing migration as part of hybrid warfare against Warsaw.