MOSCOW, May 25 (Xinhua) -- Russia's Federal Security Service (FSB) said Monday that explosive devices resembling magnetic sea mines had been found on the hull of a vessel arriving from Belgium at the port of Ust-Luga in Russia's Leningrad Region.

The devices were discovered near the engine room area during an inspection of the vessel's underwater section.

The devices were believed to have been manufactured with industrially produced components and were "presumably made in one of the NATO countries," the FSB said.

It added that each device contained about 7 kg of plastic explosives. ■