The company, CMA CGM, said it was a victim of a false cargo declaration. The shipper -- who the company identified as an Iranian trader -- had listed the materials inside the containers as "packages of glass wool and pallets of stone."

The containers in question were loaded in Bandar Abbas, a port in southern Iran, and discharged in Lagos in July, the company said. They were then transferred to a depot.

Last week, the shipper asked that the containers be re-loaded and sent to Gambia, CMA CGM said in a statement, adding that the trader had obtained the necessary documentation and clearance for customs.

Authorities in Nigeria intervened before the containers were moved.

Nigeria's security service said earlier this week that it had seized 13 shipping containers in the Lagos port filled with illegal weapons, including rockets, grenades and bullets. Each shipping container carries 20 wooden crates.

The seizure comes as Nigeria prepares for the 2011 elections, which analysts say are likely to be some of the most controversial and potentially most violent elections in the country's history.