NATO issued a warning to Moscow on Tuesday, saying it would use all means to defend against any further breaches of its airspace after the downing of Russian drones over Poland earlier this month and Estonia's report of an intrusion by Russian fighter jets last week.
The 10 September incident in Poland was the first direct encounter between NATO and Russia since its full-scale invasion of Ukraine began in early 2022.
Estonia said three Russian MiG-31 fighter jets entered its airspace for 12 minutes on Friday without authorisation, a charge that the Kremlin has rejected.
The incidents caused widespread consternation among leaders across Europe, raising questions about the alliance's preparedness against growing Russian aggression.
"Russia should be in no doubt: NATO and Allies will employ, in accordance with international law, all necessary military and non-military tools to defend ourselves and deter all threats from all directions," the alliance said in a statement.
"We will continue to respond in the manner, timing, and domain of our choosing," NATO said, underlining its commitment to Article 5 of its founding treaty that an attack on any one ally must be considered an attack on all.
The alliance provided no details about what measures they might take.
The statement comes after Estonia requested formal consultations under Article 4 of NATO's treaty, which requires a meeting whenever one of the alliance members believes its territorial integrity, political independence, or security is threatened.
On Monday, Prime Minister Donald Tusk said that Warsaw would "without discussion" shoot down flying objects when they violate Polish territory.
It's unclear whether other allies endorse this approach.
Following the violation of Polish airspace, NATO Secretary General Mark Rutte announced the formation of the Eastern Sentry programme, which aims to deter further Russian incursions and show solidarity with Poland.
"We see drones violating our airspace. Whether it was intentional or not, it is unacceptable. The allies have expressed full solidarity with Poland. It is crucial to counter aggression and defend every member of the Alliance," the NATO chief said.
Incidents in Denmark and Norway
Meanwhile on Tuesday, Denmark's Prime Minister Mette Frederiksen said Russian involvement could not be ruled out after Copenhagen airport was forced to close for several hours on Monday night following the sighting of a number of drones.
"It says something about the times we live in and what we as a society must be prepared to deal with," Frederiksen said.
The Kremlin spokesperson Dmitry Peskov called the allegations "unfounded."
Also on Monday night, Oslo airport in Norway was closed for three hours after possible drone sightings were reported.
Russia allegedly violated Norway's airspace three times in 2025, according to the government, but it remains unclear whether Monday's incident was deliberate or the result of navigation errors.
"Regardless of the cause, this is not acceptable," Prime Minister Jonas Gahr Støre said.
