A powerful explosion went off in the Sea of Azov near Mariupol, Donetsk region, at about noon on Tuesday, the city website 0629 reported.

The sound of the explosion came from the sea and was heard by residents of the Prymorsky and Zhovtnevy districts of the city. "The shockwave rattled the windows," the website said.

Spokesman for the anti-terrorist operation Dmytro Horbunov told 0629 that the blast had gone off in the sea beyond the 20-mile zone. "None of the Ukrainian border guards or naval personnel was hurt. The incident is being investigated," it said.