Lithuania has summoned a Russian diplomat to express its discontent regarding what it claims was an incursion of two Russian aircraft into its airspace on Thursday, a claim that Russia disputes.

According to a brief statement from Lithuania’s military, a Sukhoi SU-30 fighter jet and an IL-78 refueling aircraft originating from the Russian exclave of Kaliningrad entered Lithuanian airspace for a distance of 700 meters (2,300 feet) and exited after 18 seconds, likely during aerial refueling exercises.

Later that day, the Lithuanian foreign ministry confirmed it had called in the Russian embassy’s chargé d’affaires to file a formal complaint. Vilnius demanded that Russia provide an “immediate explanation” for this alleged breach of its airspace and called for “all necessary steps to be taken to prevent such occurrences in the future,” according to the announcement.

In response, Russia’s defense ministry refuted the claims of an airspace violation, asserting via Telegram that “the flights were carried out in full compliance with regulations for using airspace over Russian territory,” adding that the aircraft maintained their scheduled route and did not infringe upon the borders of other countries.

In the wake of the aircraft’s entry into Lithuanian airspace, two Spanish Air Force Eurofighter Typhoon jets, part of a NATO air patrol operation in the Baltic region, were deployed.

The three Baltic nations—each a NATO member and staunch backer of Ukraine—share borders with Russia and/or its ally Belarus and have frequently experienced airspace violations by Russian aircraft or drones.

In September, three Russian MiG-31 fighter jets entered Estonian airspace over the Gulf of Finland, remaining there for about 12 minutes. This incident prompted Tallinn to call for an urgent session of the UN Security Council and activate Article 4 of the North Atlantic Treaty, which facilitates consultations among allies in response to threats to any member state.