A large military drone crashed on the outskirts of the Croatian capital Zagreb on Thursday night, Prime Minister Andrej Plenković confirmed.
There were no reported injuries but a loud blast was heard from the crash.
The unmanned Soviet-era drone entered Croatia from the east, crossing Hungarian airspace, Plenković said while at an EU meeting in Versailles.
He said it was unclear if it came from Russian or Ukrainian forces.
Military experts from the magazine the War Zone however identified the missile-like drone as a Tuk-141, currently in use by Ukrainian forces.
Croatia's national security council met with defence and security ministers and said a criminal investigation was under way.
The drone entered Croatian airspace from Hungarian airspace at a speed of 700 kilometres per hour and an altitude of 1300 metres, the government said.
The government added that it would work with NATO to determine the circumstances.
Zagreb mayor Tomislav Tomašević said it was crucial "to determine who piloted the aircraft and where it came from and to ensure that it never happens again".
He said parts of the flying object are scattered in several locations and that it was amazing that no one was hurt.
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