Russia and Belarus on Friday launched a long-planned joint military exercise involving thousands of troops that has raised concern in the West.

The exercises, dubbed “Zapad 2025,” or “West 2025,” are held in Belarus and Russia and will last through Tuesday. They are intended to showcase close defense ties between Moscow and Minsk, as well as Russia’s military might as it fights its 3½-year-old war in neighboring Ukraine.

The maneuvers follow Wednesday’s incursion of Russian drones into Polish airspace earlier this week that fueled longstanding fears that the hostilities in Ukraine could trigger a wider conflict. The Russian military said it wasn’t targeting Poland, and Belarus suggested drones veered off course, but European leaders described it as a deliberate provocation, forcing NATO allies to confront a potential threat in its airspace for the first time.

The Russia-Belarus exercises also have drawn worries in Kyiv and its Western allies of Latvia, Lithuania and Poland, which border Belarus. When Russian President Vladimir Putin sent troops rolling into Ukraine on Feb. 24, 2022, many of them crossed from Belarus following joint drills days before the attack.

Belarusian defense officials initially said about 13,000 troops would participate in the exercise that was to take place near its western border. In May, however, its Defense Ministry said the number would be cut nearly in half, and that the main maneuvers would take place deeper inside the country.

In Moscow, the Defense Ministry said Friday that parts of the exercise will be held on the Russian territory, as well as as the Baltic and the Barents Seas.

Last month, Defense Minister Viktor Khrenin said most of the drills will happen around the city of Barysaw, about 74 kilometers (46 miles) northeast of Minsk, although some “small units will carry out practical tasks to repel a hypothetical enemy” in areas close to the border with Poland and Lithuania.

Khrenin noted that the troops will practice “planning the use of” Russian nuclear weapons and the new nuclear-capable Oreshnik intermediate range missiles that Moscow has promised to station in Belarus.

In December, Russia and Belarus signed a pact giving Moscow’s security guarantees to its ally, including the possible use of Russian nuclear weapons to help repel any aggression.

Belarus’ President Alexander Lukashenko has allowed Russia to deploy some of its tactical nuclear weapons to his country. Lukashenko also has proposed to host Russia’s latest Oreshnik intermediate-range ballistic missile that Moscow used for the first time in November against Ukraine.

Putin has said that Oreshnik missiles could be deployed to Belarus in the second half of 2025, adding they will remain under Russian control but Moscow will allow Minsk to select targets.

Belarus also sent formal invitations to all member states of the Organization for Security and Cooperation in Europe and nine countries with NATO military attaches in Minsk to monitor the drills.

Lukashenko, who has ruled Belarus with an iron hand for over 30 years, recently signaled willingness to mend his relationship with the West, which has been severely strained for years over his brutal crackdown on dissent and his support for Russia’s war in Ukraine.

The past year has seen regular releases of political prisoners and public calls for a rapprochement with the West. Last month, Lukashenko spoke by phone with Trump, who called him a “highly respected President” in a social media post, a stark contrast from other Western leaders, who have largely shunned the Belarusian.

On Thursday, Belarus freed 52 political prisoners as part of a deal brokered by the United States, which lifted some sanctions on the country’s national airline.