The seven were among 15 Russian sailors charged with illegally bringing weapons into Nigeria last year, after Nigerian authorities intercepted a ship on October 23 and found on board several guns and thousands of rounds of ammunition.
Confirming the verdict, defense lawyer Ogidigba Mobosa also told Reuters TV that two Nigerians who had been aboard the ship had been charged with wrongfully telling the Russians they had permission to enter Nigerian territory with the weapons.
The boat was operated by Nigerian shipping company Blue Sea Maritime.
Arms smuggling to and through Nigeria is rife, with demand fuelled by an Islamist rebellion in the north and by armed robbery, kidnapping, oil theft and piracy in the south.
Nigeria is also sometimes used as a conduit for shipping arms to other conflict-ridden parts of West Africa.
Shippers complain that a lack of permission for armed private security leaves them vulnerable to pirates. West Africa has overtaken Somalia's coast as the region of the continent worst affected by piracy, experts say.
During the court hearings, the Russian sailors did not explain why the arms were on board their ship.
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