Russia has been accused of jamming the GPS of the airplane carrying Ursula von der Leyen during her official visit to Bulgaria on Sunday.
The incident, first reported by the Financial Times, forced the plane to land at the city of Plovdiv using paper maps, rather than the conventional electronic system.
"We can confirm there was GPS jamming, but the plane landed safely in Bulgaria. We have received information from Bulgarian authorities that they suspect that this was due to blatant interference by Russia," a Commission spokesperson said on Monday.
"We are aware and used to somehow to the threats and intimidations that are a regular component of Russia's hostile behaviour. This will only reinforce even further our unshakable commitment to ramp up defence capabilities and support for Ukraine."
Von der Leyen was aboard a charter flight, as leaders of the EU institutions do not have official aircraft at their disposal.
There was no change in the scheduled route as a result of the incident.
The Kremlin's spokesperson Dmitry Peskov denied Russia's involvement, telling the Financial Times: "Your information is incorrect."
Von der Leyen's visit to Bulgaria was part of her tour of member states that border Russia and Belarus, aimed at expressing solidarity and promoting the European Union's €800-billion plan to ramp up defence spending.
"We have to keep up the sense of urgency," she said in Bulgaria, speaking next to Prime Minister Rosen Zhelyazkov.
"Putin has not changed, and he will not change. He is a predator. He can only be kept in check through strong deterrence."
Russia has been repeatedly accused of jamming and spoofing GPS systems across Eastern Europe. The interference is considered a form of hybrid warfare launched by the Kremlin in retaliation for European support for Ukraine. It also encompasses sabotage of underwater cables and campaigns of instrumentalised migration.
The incident comes less than a week after the shock wave of a Russian strike severely damaged the EU delegation in Kyiv. Von der Leyen said she was "outraged" by the attack and promised to tighten economic sanctions against Moscow.
This article has been updated.
