L-39 jets based at Balchik were ready to fire their onboard weapons on the three drones that attacked a container ship off the town yesterday, if the drones entered territorial waters. They did not need to take off, prime minister Rumen Radev said.

On 20 October, a US Poseidon aircraft patrolled over the Black Sea after drone attacks on merchant ships off the Bulgarian and Romanian coasts became more frequent.

More on this story: US Poseidon plane patrols over Varna after drone attacks on ships

Radev called the drone video "very good" and said it has been given to allies. Experts are running all kinds of checks. If the origin of the drones is proven, the foreign minister will formally summon the ambassador of the country concerned and hand over a protest note.

Bulgaria has told its allies. It raised the issue at the UN podium and with the UN secretary general, the NATO secretary general, the president of the European Commission and the president of the European Council. There is also a regional initiative by all ministers. All the armed forces' capabilities have been mobilised, along with those of allies.

The prime minister said any action depends on the weather, because it is not always possible to fly and act. Ships are few and their capabilities limited, so a constant watch across the whole exclusive economic zone is not possible. There are also many limits on surveillance, reconnaissance and detection, and above all on acting deep inside the zone.

"Even if we have the means to act, in legal terms we cannot operate outside our territorial waters," Radev said. He said action there would break international law. He expects an answer at last, and clear factual proof of who is behind the attacks.

The prime minister believes Bulgaria's capabilities are exhausted and the attacks will stop only with peace and peace talks. The only 100% guarantee is a ceasefire.

Radev said there is already political will for dialogue: Finnish president Alexander Stubb and the Norwegian prime minister have started to initiate talks with president Putin. The EU and NATO must move in the same direction.