A customs official at the Incheon Regional Customs displays black soybeans hidden in ton bags labeled as containing urea water solution on Thursday. (Yonhap)

Smugglers who attempted to disguise 230 tons of black soybeans, known as “seoritae,” from China as an additive for diesel engines, have been arrested, customs officials said Thursday.

The Incheon Regional Customs said it has referred 11 suspects to prosecutors without detention for alleged violations of customs law. The authorities have also issued wanted notice for two accomplices who are believed to be in China.

The suspects are accused of smuggling 230 tons of black soybeans, worth 1.3 billion won ($930,255), into South Korea in 19 separate shipments between November last year and March.

The suspects reportedly picked black soybeans, which are popular in South Korea for their purported health benefits -- they are believed to prevent cancer, aging and hair loss. They falsely declared the soybeans as urea solution or urea granules to avoid a hefty 487 percent tariff imposed on imported black soybeans.

High tariffs are levied on certain agricultural products like black soybeans to protect domestic farmers.

The smugglers believed they could avoid a customs inspection if they disguised the beans as urea, exploiting the recent domestic shortage in Korea of the chemical, which is used to reduce diesel engine emissions and agricultural fertilizers.

To further hide their scheme, the smugglers filled the lower compartments of shipping containers with black soybeans and covered them with urea solution or urea granules on top, according to customs officials.

The authorities uncovered the operation during an inspection and tracked the smuggled goods through closed-circuit cameras at a warehouse, and eventually were able to arrest the group.

The investigation also found that a representative of an agricultural cooperative bought 56 tons of the smuggled black soybeans and sold them as domestic produce.