The vessel, which belonged to the Moran group of Moscow and was flying a Dutch flag, was intercepted over the weekend in Lagos, Navy spokesman Commodore Aliyu Kabiru said by telephone, according to Reuters.
There was no immediate comment from Moran.
"The vessel was carrying 8,598 ammunitions and different rifles. Investigations are still ongoing," he said. He gave no further details.
A Navy source, who could not be named, said 22 Benelli MR1 rifles and several other automatic weapons were found.