EU chief Ursula von der Leyen first called to create a "drone wall" to counter Moscow last month, hours after NATO jets shot down Russian unmanned aircraft in Poland.

The initial focus of the proposal was on bolstering the EU's eastern border states but it has since been broadened out after mysterious drones rattled a string of countries further west.

Officials told AFP that Brussels wants the project -- now called the "European Drone Defence Initiative" -- to begin initially working by the end of 2026, and to be fully functioning by the end of 2027.

The initiative is one of several flagship EU projects set to be unveiled by the European Commission Thursday in a roadmap aimed at preparing the bloc for a potential attack by Moscow by 2030.

Alongside the drone proposal is a broader "Eastern Flank Watch" programme designed to bolster air defences along the EU's border closest to Russia.

EU defence ministers are expected to hold preliminary discussions on the roadmap Wednesday evening, and officials want leaders to give their backing at a summit next week.

The EU is seeking to tap Ukraine's war-tested expertise to incorporate low-cost capabilities to tackle drones -- but the two-year timeline to complete the project remains ambitious.

So far the EU has not given a concrete estimate for how much it thinks the drone project would cost.

Von der Leyen's initial "drone wall" proposal met some scepticism from countries such as Germany and sparked worries that Brussels could be treading on NATO's toes.

Germany and France are reluctant for the EU's executive to take too central a role in military planning, which is the preserve of member state governments.

Countries in the south of the bloc have also pressed for the drone initiative to not just be focused on the EU's eastern nations.

Von der Leyen said earlier this month that the drone initiative would be broadened out and could help tackle other issues such as illegal migration.