Since then, similar incidents have been reported in Germany, Denmark, Norway and the Baltic states, the AP reports.

Unauthorized air incursions into NATO airspace have become a major source of concern for allies, raising questions about the alliance's preparedness against Russia and sparking discussions about the need for a"drone wall" along European borders.

Poland, Germany, Estonia, Denmark and Norway

On September 10, a swarm of Russian drones flew into Polish airspace, forcing NATO aircraft to rush to intercept them and shoot down some of the devices. It was the first direct encounter between NATO and Moscow since Russia launched all-out war against Ukraine on February 24, 2022.

A few days later, NATO planes escorted three Russian fighter jets out of Estonian airspace.

In Germany, Munich Airport was closed twice in early October due to drone sightings.

In Denmark, drones flew over Copenhagen Airport on September 22, causing major disruption to air traffic at Scandinavia's largest airport. Danish Prime Minister Mette Frederiksen called the incident"the most serious attack on Danish critical infrastructure ever," and did not rule out Russian involvement.

In Norway, a drone was reported at Oslo Airport that same evening, forcing all flights to use a single runway. Authorities are investigating possible links between the two incidents.

What is known from the reports

Drones flew over four smaller Danish airports between September 24 and 25, including two that serve as military bases. Danish Defense Minister Troels Lund Poulsen said a “professional” actor was likely behind the “systematic flights.”

Danish media reported that drones were seen near Karup Air Base, Denmark's largest military base, but the Ministry of Defense refused to confirm, citing operational security reasons.

German authorities have been investigating claims that unidentified drones have been spying on critical infrastructure in the northern state of Schleswig-Holstein. Several drones were spotted on September 25 above a power plant in Kiel, near a university hospital, near a shipyard in the port city, above the TKMS plant in Kiel, a supplier of maritime defense technology, and above government buildings and the Heide oil refinery. Other suspicious drones were spotted above a military base in Sanitz, in the state of Mecklenburg-Western Pomerania.

Other major challenges

Estonia has summoned a Russian diplomat to protest after three Russian fighter jets entered its airspace without permission and remained there for 12 minutes.

In Lithuania, on Thursday, at around 6:00 p.m., two Russian military aircraft – an SU-30 and an IL-78 refueling plane – flew into the airspace at a distance of about 700 meters. The planes flew away after about 18 seconds. The Lithuanian president described the incident as a flagrant violation of territorial integrity.

The Lithuanian Armed Forces believe the planes may have been conducting refueling exercises in the Russian exclave of Kaliningrad. Two Spanish fighter jets carrying out NATO air policing missions were sent to the area.

The Russian Defense Ministry rejected the claim, claiming that the Su-30 jets carried out training flights over Kaliningrad, strictly following the rules.

Russia denies the intention

Russia has been blamed for some of these incidents, but denies any wrongdoing. European authorities have not released many details about the drone intrusions, with some only publicly acknowledging the overflights days later.

In other cases, authorities were unable to confirm the reports. At one point, Danish authorities were inundated with 500 reports in 24 hours, some of which turned out to be just stars in the sky.

European defense ministers have agreed to develop a"drone wall" along their borders to better detect, track and intercept drones that violate European airspace.

Countries are scrambling to find solutions to respond to the situation, including whether to allow authorities to shoot down the drones. Some European officials have described the incidents as tests by Moscow to see how NATO would react, raising questions about the alliance's preparedness against Russia.