The warning follows airspace violations, sabotage, and cyberattacks Von der Leyen attributed to Moscow.

Russia is waging a "targeted grey zone campaign" against Europe, including airspace violations, sabotage and cyberattacks, that will only escalate if the Kremlin is not challenged, the European Union's top official warned on Wednesday.

European Commission President Ursula von der Leyen said that in just two weeks, fighter jets breached Estonia's airspace, while drones overflew military bases and critical infrastructure sites in Belgium, Denmark, Germany, Poland and Romania.

"It is time to call it by its name, this is hybrid warfare. And we have to take it very seriously," Von der Leyen told EU lawmakers in Strasbourg, France.