Belarus and Russia on Friday launched their joint strategic exercise “Zapad-2025”, a four-day series of drills running from 12 to 16 September across training grounds in both countries, with additional activity at sea.

Minsk and Moscow say the exercise is defensive and long-scheduled; NATO members on the eastern flank have increased vigilance following this week’s drone incidents over Poland.

Russia’s defence ministry said the drills involve command-and-control training and coordinated operations by regional coalition forces. The exercise includes activity in the Baltic and Barents seas in parallel with land manoeuvres. Belarus’s defence ministry described the stated objective as practising joint actions to ensure the Union State’s military security and to repel a potential attack.

Officials in Minsk have previously characterised “Zapad-2025” as a planned event in a regular cycle, echoing Russian statements that it is not directed against any other state. The Belarusian side has stressed the drills’ “defensive” framing.

Reporting ahead of the start date indicated that scenarios would include training related to nuclear weapons employment and drills around Russia’s intermediate-range “Oreshnik” missile system, which Russian and Belarusian officials have discussed in recent briefings. Neither side has published full scenario details.

The start of “Zapad-2025” follows a sequence of incidents that sharpened allied attention. Between 9 and 11 September, Polish authorities reported multiple incursions by Russian drones into Polish airspace during overnight strikes on Ukraine. NATO aircraft assisted in the response. Warsaw has sought consultations with allies and requested an emergency meeting of the UN Security Council.

Poland has closed all crossings on its border with Belarus “until further notice”. The closure took effect from 00:00 on 12 September local time (22:00 GMT on 11 September), according to Polish and Belarusian official communications. Freight and passenger traffic in both directions has been halted.

In parallel, Poland has imposed restrictions on air traffic along sections of its eastern frontier, banning drone operations and limiting small, non-commercial aviation near the borders with Belarus and Ukraine. The measures are currently scheduled to remain in force until 9 December.

Latvia has restricted its airspace along a 50-kilometre strip of its eastern border with Russia and Belarus from 18:00 on 11 September until at least 18 September, with the possibility of extension. Riga cited the drone incursions into Poland as the trigger for the move.

Separately, Latvia’s Saeima voted on Thursday to advance a draft decision enabling a full closure of the country’s land borders with Russia and Belarus for the period of the exercise. The proposal was referred to the National Security Committee for consideration.

The Russian and Belarusian authorities have framed “Zapad-2025” as routine. However, the timing—two days after the drone incidents over Poland—and the geographic spread of the exercise have drawn scrutiny from allied governments. Western officials and analysts are monitoring for indicators of force posture, logistics and command arrangements relevant to the Union State’s warfighting concepts.

Open-source assessments published in recent days note that the active phase from 12 to 16 September is the first “Zapad” iteration held during Russia’s full-scale war against Ukraine. Earlier analytical briefs anticipated that elements would be staged deeper inside Belarus than in some previous cycles, though official releases on Friday placed the emphasis on multiple training areas across both states and at sea.

Headcounts have not been uniformly disclosed. Some official and media statements ahead of the drills cited an indicative figure of around 13,000 personnel, consistent with previous patterns of declared participation for large exercises, though independent estimates often suggest wider activity across parallel events.

NATO members, particularly on the alliance’s north-eastern flank, are conducting their own training during September. Polish and Lithuanian forces began exercises earlier this month with allied participation, and Germany has said it will intensify air policing over Poland in light of recent events.

Minsk has invited foreign military attachés to observe parts of the exercise, according to regional reporting, while reiterating that the scenario is centred on repelling aggression against the Union State. As with previous “Zapad” cycles, regional authorities will watch for any changes in Russian deployments that outlast the exercise window.