European Commission President Ursula von der Leyen said that in just two weeks, fighter jets had breached Estonia's airspace, while drones overflew military bases and critical infrastructure sites in Belgium, Denmark, Germany, Poland and Romania.
"Europe must respond. We must investigate every incident, and we must not shy away from attributing responsibility, because every square centimetre of our territory must be protected and safe," von der Leyen told EU politicians in Strasbourg, France.
"If we hesitate to act, the grey zone will only expand," she said on Wednesday.
The EU's executive branch, under von der Leyen's guidance, is preparing a plan for Europe to be ready to confront such challenges by 2030.
EU officials believe Russia could be capable of launching an attack on another European country within three to five years.
The plan includes the development of a "drone wall" of high-tech systems linked to equipment that can detect, track and destroy drones, as well as strike their operating systems or pilots on the ground.
In two weeks, von der Leyen will submit a "road map" for bolstering Europe's defences by the end of the decade to the 27-nation bloc's heads of state and governments for their approval.
Von der Leyen said it was simply not affordable for European countries to continue to scramble the latest-generation fighter jets to counter relatively cheap drones, as happened when several of them entered Polish airspace a month ago.
"This is absolutely not sustainable. We need an anti-drone system that is affordable and fit for purpose. For swift detection, swift interception, and when needed, swift neutralisation," she said, adding that Europe had much to learn in this from Ukraine.
The commission believes that the best way to encourage European countries to invest more in defence is to ensure that it creates jobs and is good for business in Europe.
It insists that at least 65 per cent of any project funded with EU money should be based on the continent.
In recent years, the member nations have placed about two-thirds of their orders with US defence companies.
At a summit in Copenhagen last week, the position of some EU leaders towards the drone incidents, acts of sabotage, cyber attacks and sanction-busting appeared to have hardened.
Denmark has not directly attributed a series of drone flights over the country in recent weeks to Russia.
French President Emmanuel Macron said Europe must take a more aggressive approach with Russia by shooting down drones that enter European airspace and boarding shadow fleet ships illicitly transporting oil to deprive Moscow of war revenue.
