Attacks in the Black Sea mean Bulgaria must strengthen its defences faster, say reserve colonel Vladimir Milenski and Todor Ivandzhikov, chair of the Bulgarian Aviation Industry Association.

The German surface-to-air missile systems that parliament voted to buy do not work against drones, Milenski said. He said they were meant for a specific military situation and task, different from the current one.

He said the problem is slow deliveries of defence equipment and the state's failure to adapt to a fast-changing military situation.

The authorities' response to the attacks is weak, Milenski said. Bulgaria needs a long-term strategy, not steps that come only after an incident. He said the government is not even tactical and reacts only after it is hit.

Ivandzhikov welcomed Bulgaria joining NATO's anti-drone initiative. The state, business and science need to work more closely together, he said.

The mobile anti-drone systems Bulgaria has now have a short range and do not give full protection, Ivandzhikov said. He said the country needs radars, sensors and satellites linked in one network.

Journalist Yulia Bahovski said the Romanian president believes the attacks involve aerial drones. Romanian institutions and the public do not communicate in a coordinated way, which makes it hard to draw conclusions, she added.

Romania is discussing invoking Article 4 of the NATO treaty, but Bahovski said she has not heard an official position from any responsible official.