In a post on X, Lithuania's President Gitanas Nausėda slammed what he called a "blatant breach of international law and territorial integrity."
Two Russian military aircraft entered Lithuania's airspace on Thursday for about 18 seconds, the country's military said on Thursday.
The two aircraft, identified as an Su-30 fighter jet and an Il-78 refuelling tanker, were thought to have been on a refuelling training mission when they crossed the border into NATO member Lithuania at around 1600 CET from the Russian exclave of Kaliningrad.
Spanish Eurofighter Typhoon jets from NATO's Baltic Air Police were scrambled and are patrolling the area, the military said in a statement.
In a post on X, Lithuania's President Gitanas Nausėda slammed what he called a "blatant breach of international law and territorial integrity."
"I strongly condemn the violation of Lithuanian airspace recently by the fighter jet and transport plane of Russian Federation from Kaliningrad region," Nausėda said in a video.
"We have to react to this."
There was no immediate comment from Moscow.
Both NATO and the European Union have been on high alert following a string of airspace violations, thought to be from Russia, in recent weeks.
NATO issued a warning to Moscow at the end of September, saying it would use all means to defend against any further breaches of its airspace after the downing of Russian drones over Poland and Estonia's report of an intrusion by Russian fighter jets.
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.
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 23 September, Denmark's Prime Minister Mette Frederiksen said Russian involvement could not be ruled out after Copenhagen airport was forced to close for several hours the previous 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 22 September, 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.