TALLINN, Estonia (AP) — Belarus began military exercises Monday near its border with Poland and Lithuania, a move coming with tensions already heightened with the two NATO members over Russia-linked Wagner mercenaries moving to Belarus after their short-lived mutiny in Russia.

Both Poland and Lithuania have increased border security since thousands of Wagner fighters arrived in Russian-allied Belarus under a deal that ended their armed rebellion in late June and allowed them and their leader, Yevgeny Prigozhin, to avoid criminal charges.

Leaders of the two NATO nations have said they are braced for provocations from Moscow and Minsk in a sensitive area where both countries border Belarus as well as the Russian exclave of Kaliningrad. They commented early in August after two Belarusian helicopters flew briefly at low altitude into Polish air space. Belarusian authorities denied their helicopters entered Poland.

The Belarusian Defense Ministry said the drills that began Monday are based on experiences from “the special military operation” — the term Russia uses for its war in Ukraine. It said that includes the “use of drones as well as the close interaction of tank and motorized rifle units with units of other branches of the armed forces.”

The war games were taking place in the Grodno region of Belarus, near the so-called Suwalki Gap — a sparsely populated stretch of land running 96 kilometers (60 miles) along the Polish-Lithuanian border. It links the three Baltic states of Lithuania, Latvia and Estonia with the rest of the NATO alliance and separates Belarus from Kaliningrad, a heavily militarized Russian exclave on the Baltic Sea that has no land connection to Russia.

Military analysts in the West have long viewed the Suwalki Gap as a potential flashpoint area in any confrontation between Russia and NATO. They worry that Russia might try to seize the gap and cut off the three Baltic states from Poland and other NATO nations.

Belarus’ military has said it is actively using Russian mercenaries to train its troops, and the exercises began as more Wagner fighters reportedly arrived in the country. According to Belaruski Hajun, an activist group that tracks troop movements in Belarus, mercenaries arrive in small groups daily.

Grey Zone, a Wagner-linked blog on the messaging app Telegram, reported Monday that some 7,000 Wagner fighters are at a camp close to Asipovichy, a town 230 kilometers (140 miles) north of the Ukrainian border. The claim could not be independently verified.