Drone attacks in Bulgaria's exclusive economic zone will be on the agenda when EU leaders meet in Brussels on 15 and 16 October, a European Council spokesperson told Bulgarian National Radio.
The summit follows hybrid incidents blamed on Russia, including some off the Bulgarian and Romanian coasts of the Black Sea. The spokesperson said similar cases have built up over months. One was the attack on Leipzig airport.
European Council president António Costa says in his invitation to leaders that next week they will take up Russia's "increasingly reckless behaviour, including its campaign of hybrid attacks across Europe".
A US Congress report earlier this month also pointed to the region's weak spots. It says Bulgaria was the target of at least four Russian attacks between 2018 and 2025.
At the end of September, the European Commission proposed an EU version of Article 4 of the Nato treaty, after a rise in security incidents. Under it, any EU country facing a hybrid threat could draw in the others.
Ukrainian president Volodymyr Zelensky will also speak to the leaders. He will set out his country's current military needs. Leaders will also review how far Ukraine has come on its path to EU membership. More negotiating clusters are expected to open before the summit.