A Soviet-era scouting drone flying across Hungary from Ukraine crashed near the Croatian capital of Zagreb, leaving a big hole in the ground, the Croatian government said on Friday.
No deaths or injuries were reported.
An explosion was heard near Lake Jarun in Zagreb at around 11 p.m. on Thursday, Croatian media reported. Two parachutes were found and several vehicles had been damaged, police said.
The drone, flying at 1,300 meters, came from Hungary and crashed seven minutes after entering Croatia's air space, the government said. Both Hungary and Croatia are NATO members.
Croatian President Zoran Milanovic said that according to preliminary information the drone originally came from Ukraine and crashed once it had run out of fuel.
"We estimate that this was an incident and it was not (military action) directed against Croatia," Milanovic said.
Defense Minister Mario Banozic declined to comment on details.
"This was a very serious incident. We will have to investigate it thoroughly," Banozic told press conference.
He said it was unclear whether the drone belonged to Russia or Ukraine. He also declined to say from where the drone could have originated.
"The investigation will reveal further details," he said.
Russia invaded Ukraine two weeks ago. Russian forces bearing down on the capital Kyiv were regrouping northwest of the city, satellite pictures showed, and Britain said Moscow could now be planning an assault within days.
Hungarian Foreign Minister Peter Szijjarto said Hungary was closely cooperating with Croatia and other NATO allies over the drone.
"Our authorities are examining what happened, as according to present data, the air space of several NATO members including Hungary was affected by the drone's flight."