Nigerian authorities seized a ship and arrested its 15 Russian crew members on suspicion of arms smuggling after they found several guns and about 8,500 rounds of ammunition on the boat, the navy said Tuesday.
The vessel was intercepted over the weekend in Lagos, one of Africa's busiest ports, navy spokesman Commodore Aliyu Kabiru said by telephone.
It belonged to the Moran Security Group, based in Moscow, and was flying a Dutch flag, he added.
There was no immediate comment from Moran.
Arms smuggling is a flourishing enterprise in Nigeria, which is battling an Islamist insurgency in the north.