A swarm of Russian drones entered Polish airspace, which officials described as a deliberate provocation.
NATO responded by strengthening its air defenses on its eastern flank.
Moscow has shown off conventional and nuclear military might in long-planned drills with Belarus, warning the West not to send foreign troops to Ukraine.
All of these events come a month after a US-Russian summit in Alaska failed to bring peace to Ukraine and only exacerbated tensions in Eastern Europe.
When Russian President Vladimir Putin began the full-scale invasion of Ukraine in February 2022, this happened just days after joint exercises with Belarus. Another major exercise, dubbed "West 2025", has unsettled NATO members Poland, Latvia and Lithuania, which border Belarus.
The exercises, which ended yesterday, involved nuclear-capable bombers and warships, tens of thousands of troops and thousands of combat vehicles, simulating a joint response to an enemy attack - including, officials said, planning for the use of nuclear weapons and options involving Russia's new Oreshnik intermediate-range ballistic missile.
NATO Secretary-General Mark Rutte, referring to Moscow's hypersonic missiles, said they shattered the notion that Spain or Britain were safer than Russia's neighbors Estonia or Lithuania.
"Let us come to a common understanding that within this 32-member alliance we all live on the eastern flank," he said in Brussels.
Last September, Putin unveiled a revision of Moscow's nuclear doctrine, noting that any conventional attack on Russia by a nuclear-armed state would be considered a joint attack on his country. The doctrine was clearly aimed at dissuading the West from allowing Ukraine to strike Russia with longer-range weapons and appears to significantly lower the threshold for the possible use of Russia's nuclear arsenal.
The doctrine also places Belarus under Russia's nuclear umbrella. Russia, which claims to have deployed nuclear weapons in Belarus, plans to deploy Oreshnik missiles there later this year.
The Zapad 2025 exercise comes as Russia's three-and-a-half-year war in Ukraine continues despite pressure from US President Donald Trump for a peace deal and his meeting with Putin on August 15 in Alaska.
On September 10, two days before the start of the exercises, about 20 Russian drones entered Polish airspace. While Moscow denied directing the drones towards Poland and officials in Belarus claimed the drones had deviated from their course after their signal was jammed by Ukraine, Polish Prime Minister Donald Tusk said it was a "provocation" that "brings everyone closer to open conflict, more imminent than at any time since World War II.".
Rutte described Moscow's actions as "reckless" and announced a new NATO mission to secure the airspace on the eastern flank of the pact, "Eastern Sentry".
While NATO allies in Europe rejected Belarus' offer to send observers to the exercises, American military observers showed up there, apparently reflecting the ongoing rapprochement between the United States and Belarus. Last week, Belarus released 52 political prisoners as part of a Washington-brokered deal that lifted some sanctions on the country's national airline.
When Russia first used the "Oreshnik" against Ukraine in November 2024, Putin warned the West that it could use it against Kiev's allies who allow it to strike Russia with its longer-range missiles.
Putin boasted that the "Oreshnik"'s multiple warheads They descend at speeds of up to Mach 10 and cannot be intercepted, and a few of them, used in a conventional strike, could be as destructive as a nuclear attack. Russian state media noted that the missile could reach an air base in Poland in just 11 minutes, and NATO headquarters in Brussels in 17 minutes. There is no way to tell whether the missile is carrying nuclear or conventional warheads before it hits its target.
Russia has begun mass production of the "Oreshnik", Putin said last month, confirming plans to deploy the missiles in Belarus later this year.
Belarusian Deputy Defense Minister Pavel Muraveyko said yesterday that the exercises include planning the use of tactical nuclear weapons and the deployment of "Oreshnik". He did not give further details.
Unlike intercontinental ballistic missiles with nuclear warheads that can destroy entire cities, the less powerful tactical nuclear weapons have a short range and are used against troops on the battlefield.
The Russian Defense Ministry released videos of nuclear-capable bombers on training missions as part of the exercises, which took place in Belarus, which borders NATO members Poland, Latvia and Lithuania, to the Arctic, where Russia's navy conducted training launches of missiles capable of carrying nuclear warheads, including the hypersonic "Zircon" missile.
Putin, who donned military uniform on Wednesday to visit part of the exercises in Russia, said about 100,000 soldiers were taking part in the maneuvers, along with 10,000 combat vehicles and weapons systems. at 41 test sites.
Belarusian President Alexander Lukashenko said in December that his country had several dozen Russian tactical nuclear weapons.
The revised Russian nuclear doctrine states that Moscow could use nuclear weapons "in the event of aggression" against Russia and Belarus with conventional weapons that threaten "their sovereignty and/or territorial integrity."
Russian and Belarusian officials have so far made contradictory statements about who controls the weapons. When the deployment was first announced, Lukashenko said Belarus would be responsible for them, but the Russian military command stressed that it would retain control.
At the signing of the security pact with Lukashenko in December, Putin said that even if Russia controlled the Oreshnik missiles, Moscow would allow Minsk to choose the targets. He noted that if the missiles were used against targets closer to Belarus, they could carry a significantly larger payload.
The deployment of tactical nuclear weapons in Belarus would allow Russian aircraft and missiles to reach potential targets in Ukraine more easily and quickly, should Moscow decide to use them. It also expands Russia's ability to attack several NATO allies in Eastern and Central Europe.
"Deploying the weapons closer to the Western borders sends a signal, even if there are no plans to use them," said Andrei Baklitsky, a senior fellow at the United Nations Institute for Disarmament Studies.
Alexander Alesin, a military analyst in Minsk, said that the deployment of Russian tactical nuclear weapons in Belarus has turned it into a "balcony overlooking the West" that threatens the Baltic states and Poland, as well as Ukraine.
The planned deployment of "Oreshnik" would become a threat to all of Europe, returning it to the Cold War scenario, when Belarus was a forward base for Soviet nuclear weapons aimed at Europe, the analyst said.
During the Cold War, Belarus housed more than half of the Soviet arsenal of medium-range missiles under the cover of its dense forests. Such ground-based weapons with ranges of 500 to 5,500 kilometers were banned under the 1987 Intermediate-Range Nuclear Forces Treaty, which was suspended in 2019.
“Belarus served as a nuclear fortress during the Soviet Union“, Alesin said.
The Soviet Union had built about 100 heavily fortified nuclear weapons storage facilities in Belarus, some of which were converted to store Russian nuclear weapons, the analyst added.
“If they have restored several dozen storage facilities and actually store nuclear warheads in only two or three of them, a potential adversary will have to guess where they are,“ Alesin pointed out.
Translation from English: Alexey Margoevsky, BTA