The U.S. military will increase its ability observe Russian troop movements near the Baltic states during a large military exercise planned by Moscow this summer, U.S. defense officials said.

The United States will put ships in the Baltic Sea and take over the North Atlantic Treaty Organization’s air policing in the region ahead of the exercises in August and September, said the two officials, who spoke on the condition of anonymity to discuss sensitive military maneuvers.

The Russian exercise, known as Zapad, or West, occurs every four years and will take place this year in western Russia, including Belarus and the Russian enclave of Kaliningrad.

The U.S. military estimates that 70,000 to 100,000 Russian troops could take part in the exercise, the officials said, adding that the Russian military could also take the opportunity to upgrade certain equipment permanently stationed in the region. Specifically, the officials said that they expect the Russian missile defenses in Kaliningrad to be permanently upgraded with nuclear-capable Iskander ballistic missile systems.