Greece has still not received explanations from Ukraine’s defense officials on an apparently Ukrainian explosive sea drone discovered in Greek waters a week ago, Defense Minister Nikos Dendias said Thursday.

“I am still awaiting, and I await with great interest, the explanations that Ukraine’s defense minister has committed to provide our country on the drone that was found in the Ionian Sea,” Dendias said.

Fishermen discovered the large drone last Thursday bobbing against rocks on the western island of Lefkada, and towed it to port. A day later military experts defused the Ukrainian-made crewless vessel.

“This matter is extremely serious,” Dendias added. “The vessel was carrying explosives, and endangered the safety of navigation. I don’t want to think what would have happened if a passenger ferry or any other ship had collided with the drone.”

Dendias said Greece “is owed a clear explanation.”